Porsche training p80 climate control diag repair

Industry has responded with changes and improvements to A/C systems and service procedures: • Refrigerant R-12 is no longer produced or installed by manufacturers and R-134a is the only

AfterSales Training

Climate Control Systems Diagnosis & Repairs

P80

Porsche AfterSales Training

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Important Notice: Some of the contents of this AfterSales Training brochure was originally written by Porsche AG for its

rest-of-world English speaking market The electronic text and graphic files were then imported by Porsche Cars N.A, Inc and edited for content Some equipment and technical data listed in this publication may not be applicable for our market Specifications are subject to change without notice.

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© 2010 Porsche Cars North America, Inc All Rights Reserved Reproduction or translation in whole or in part is not permitted without written authorization from publisher AfterSales Training Publications

Dr Ing h.c F Porsche AG is the owner of numerous trademarks, both registered and unregistered, including without limitation the Porsche Crest®, Porsche®, Boxster®, Carrera®, Cayenne®, Cayman™, Panamera®, Tiptronic®, VarioCam®, PCM®,

Electrical Troubleshooting Logic

1 -Do you understand how the electrical consumer is expected to operate?

2 -Do you have the correct wiring diagram?

3 -If the circuit contains a fuse, is the fuse okay & of the correct amperage?

4 -Is there power provided to the circuit? Is the power source the correct voltage?

5 -Is the ground(s) for the circuit connected? Is the connection tight & free of resistance?

6 -Is the circuit being correctly activated by a switch, relay, sensor, microswitch, etc.?

7 -Are all electrical plugs connected securely with no tension, corrosion, or loose wires?

Table of Contents

Introduction i

A/C Refrigerant System Service and Diagnosis 1

Air Conditioning Basics 2

System Descriptions – Boxster (986), Boxster/Cayman (987) & 911 (996/997) 3

Cayenne (9PA) 2003 - 2010 (E1 1st & 2nd Generations) 4

Cayenne (92A) 2011 (E2) 5

Cayenne S Hybrid (92A) 2011 (E2) 6

Panamera (970) 2010 - 0n 7

Conversion Charts 8

In the past, air conditioning in automobiles was considered an option and a luxury A/C was rarely found

in high performance vehicles and the customer was willing to trade comfort for performance.

The rules have changed and today’s customer expects A/C to be an included feature High levels of performance and comfort are expected All current Porsche models sold in North America have A/C standard.

With the push of a button, today’s customer expects rapid heating and cooling Only when the system fails to function will the customer be consciously aware of it This is where you, the technician, come in.

In order to satisfy the Porsche customer’s high expectations, you will need to successfully diagnose, test and repair climate control systems in a timely manner.

After a climate control system repair, the first thing that the customer will do is operate the system Success or failure is measured in degrees.

Ozone Depletion and Global Warming

The Ozone layer is in the stratosphere 16-48 kilometers

(10-30 miles) above the Earth's surface This layer shields

the earth from much of the sun's ultraviolet radiation

Chlorine found in R-12 refrigerant released into the

atmos-phere can seriously damage the Ozone layer

Energy from the sun drives the earth's weather and

climate Sunlight heats the earth's surface, and some of

the sunlight is reflected in the form of infrared radiation

Much of this radiant energy dissipates into space, but

some is reflected back into the atmosphere Atmospheric

greenhouse gases (water vapor, Carbon Dioxide, and

other gases) trap some of the outgoing energy, retaining

heat (like the glass panels of a greenhouse) The trapping

of too much radiant heat energy is suspected to cause

Global Warming

There is strong evidence that the quantity of Carbon

Dioxide in the atmosphere and the rising average world

temperatures are related Carbon Dioxide, one of the

gases emitted by internal combustion engines, has a

significant greenhouse effect, but R-12 refrigerant in the

upper atmosphere has a Global Warming Potential (GWP)

8,500 times greater than Carbon Dioxide R-134a

refrigerant is better, but still has a GWP value of 1,300

The discovery of these problems caused the governments

of the industrialized world to establish a time table for thereduction and eventual elimination of the production of

chemicals that deplete the Ozone layer The Montreal

Protocol was enacted in September 1987, and laws were

enacted requiring the automotive service industry tomodify the servicing of A/C refrigerant systems

All refrigerants used in automotive air conditioners mustnow be recovered and recycled whenever an A/C system

is opened for service or repair Also, refrigerant R-12(FREON) is no longer produced, and has been replacedwith a less harmful refrigerant, R-134a (SUVA) R-134a isthe only alternative refrigerant for R-12 that is approvedfor use in new automobiles by all auto manufacturers.Porsche phased-in the use of R-134a in 1993 Refer topage I-21 for more refrigerant information

Any person servicing motor vehicle air conditioningsystems MUST by law be properly trained, certified anduse approved refrigerant recycling equipment Techniciansmust successfully complete an EPA approved recyclingcourse and be tested Certification is available from theNational Institute for Automotive Service Excellence (ASE)and the Mobile Air Conditioning Society (MACS) State andlocal jurisdictions may have their own certification require-ments that supersede federal requirements

A/C Refrigerant System Service & Diagnosis

A/C Refrigerant System Service Procedures .1.5

A/C System Performance Testing .1.7

Warnings and Cautions 1.10

Service Equipment Safety 1.11

First Aid 1.12

A/C Refrigerant System Service & Diagnosis

Notes:

A/C Refrigerant System Service & DiagnosisA/C Refrigerant System Service

Before 1992, automotive air conditioning services could

be performed by anyone with a manifold gauge set, cans

of refrigerant and a can tap Refrigerant was inexpensive

and considered harmless Do-it-your-selfers routinely

top-off leaking systems rather than paying for expensive

repairs

In repair shops, refrigerant was routinely vented to the

atmosphere whenever an A/C system needed to be

opened This was accepted practice At the time, the

envi-ronmental effects were unknown and methods to recover

refrigerant were not available R-12 was so inexpensive

that its complete loss and replacement was seen as

insignificant

Environmental Impact

Things changed when it was discovered that R-12 released

into the atmosphere has contributed to two serious

effects: destruction of Ozone in the stratosphere, and

global warming

The Clean Air Act legislation of 1990 included these

provi-sions:

• A/C technician certification by 1 Jan 1992

• Use of EPA certified recovery and recycling equipment

• Recovery of both R-12 and R-134a refrigerants

• Prohibits mixing refrigerants

• Provides penalties including fines up to $27,500/day

and 5 yrs imprisonment

Industry has responded with changes and improvements

to A/C systems and service procedures:

• Refrigerant R-12 is no longer produced or installed by

manufacturers and R-134a is the only approved

refrigerant installed by OEMs

• By law, technicians must be properly trained and

certified to work on mobile A/C systems

• All refrigerants used in mobile air conditioners must now

be recovered and recycled whenever an A/C system is

opened for service or repair

A/C Service Equipment

By law, all automotive repair facilities performing A/Csystem services must have approved equipment torecover and recycle refrigerant R-134a If the shop alsoservices vehicles with R-12 or any other refrigerant, itmust have separate equipment for those refrigerants aswell

All refrigerant recovery and recycling equipment must becertified to meet the Society of Automotive Engineers(SAE) standards for performance and refrigerant purity

Equipment Maintenance

A/C service equipment must be periodically maintained toreduce the possibility of refrigerant loss and inaccuratecharge

Follow the service and maintenance schedule and tions for your service equipment Maintenance items varybut in general, periodic maintenance procedures arerequired for all service equipment

instruc-Typical service procedures for refrigerantrecovery/recycling/recharging stations include:

• Vacuum pump oil change

• Filter/dryer cartridge replacement

• Checking the station for leaks

• Refrigerant storage tank scale accuracy check

A/C Refrigerant System Service & Diagnosis

Manifold Gauge Set

The port under the low side gauge connects the low side

service hose to the low side service connection on the

system The low side service hose is always blue

The port under the high side gauge similarly connects the

high side service hose to the high side service connection

on the system The high side service hose is always red

The center port on the manifold can be connected to

either the red high side or blue low side service hoses

when the respective hand valve is opened The hand

valves are opened ONLY when recovering,

evacuating or recharging refrigerant from a system.

Otherwise, the hand valves must be closed

Both high and low side gauges read system pressures

with the hand valves on the manifold closed A/C service

stations have similar gauges and hand valves They may

appear different but in most cases they work the same

way

Service hoses for R-134a systems have quick connectors

and check valves to minimize refrigerant loss when

connecting and disconnecting the hoses Some hose

connectors automatically depress the service port check

valve pin Other hose connectors have a knob which must

be screwed clockwise after the hose is connected to

manually depress the service port check valve pin

Service Ports on the Vehicle

The red and blue service hoses mate with the A/C erant service ports on the vehicle The high side and lowside service port fitting quick connectors are different toprevent reversing the hose connections

refrig-The service port fittings have spring loaded check valves

to prevent the loss of refrigerant Dust caps keep theports clean and are a secondary seal against refrigerantloss

For service port locations on the different models, see theindividual model sections (Cayenne service ports shownabove)

Notes:

A/C Refrigerant System Service & DiagnosisA/C Refrigerant System Service Procedures

The A/C service station recovers and stores the

refrigerant while the system is being repaired The service

station must recycle the refrigerant so that it is pure for

reuse Finally the service station must remove all residual

air and moisture from the system and then recharge it with

an accurately measured quantity of refrigerant

The following information explains A/C service procedures

The information generally applies to all types of service

stations Be sure to consult the operating instructions for

the specific service equipment that you are using and

always follow the safety recommendations

Recovery

To prepare for refrigerant recovery, be sure that the

engine and A/C system are OFF Attach the service hoses

to the vehicle service ports Open the service hose valves

on the quick connectors if present (not all service hoses

have them) Be sure that both high side and low side

gauge hand valves on the service station control panel are

closed

Check both gauges on the control panel before continuing

If the pressures are zero, the system is completely

discharged and may contain air DO NOT ATTEMPT

RECOVERY as this will cause air to be drawn into the

refrigerant storage tank

If the pressure gauges do not read zero, open both high

side and low side gauge hand valves on the service station

control panel Open the storage tank valves as described

in the operating instructions

Recover refrigerant per service station instructions Most

service stations will weigh the recovered refrigerant and

indicate how much refrigerant was removed Note this

value as it can help diagnosis later

The recovery process creates a shallow vacuum of about

15 in.Hg in the A/C system Usually the machine will turn

off when this vacuum is reached Wait five minutes and

watch the low side pressure gauge to see if pressure

rises Often, pressure will rise because remaining

refrigerant trapped in refrigerant oil, desiccant, etc is now

boiling off in the low pressure If pressure rises above 0

in.Hg., again perform the recovery Repeat until pressure

does not rise after five minutes

Note:

Depending on the system you’re running, deep vacuum isnot created during recovery If a deep vacuum wereachieved, any water in the system would boil at roomtemperature and be pulled into the refrigerant storagecontainer, contaminating the refrigerant and overloadingthe service station filter

Any moisture in the system will be removed later duringevacuation, when a deep vacuum is reached When therecovery operation is complete, close both high side andlow side gauge hand valves on the service station controlpanel Also close the storage tank valves

Oil Separator

While recovering, approx 15-20 cc (0.5-0.7 oz.) of erant oil may be removed from the system along with therefrigerant After recovering, measure the quantity of oil inthe oil separator Follow the instructions for your machine.This is the minimum amount of oil that must be replacedwith fresh oil when you recharge the system If anycomponent in the refrigerant circuit is replaced, more oilmay have to be added, as the oil circulates throughout thesystem and coats the inside of every component

refrig-Notes:

A/C Refrigerant System Service & Diagnosis

Evacuation

Evacuation is the process of creating a deep vacuum of

around 29 in Hg in the empty A/C system Usually this is

done after the system has been opened for repairs

Evacu-ation removes any air present and lowers the pressure in

the A/C circuit to the point where moisture in the system

boils at room temperature This water vapor will then be

removed by the vacuum pump You should evacuate a

system that has been opened for at least 15 min to be

sure all air and moisture is removed

For a quick and rough check for large system leaks, turn

off the vacuum pump as soon as it reaches more than

20-25 in.Hg Wait five minutes and observe the low pressure

gauge If gauge pressure rises, there is probably a large

leak and there is no reason to continue evacuating until it

is repaired This method will not locate very small leaks

Leak detection methods will be discussed later

Reasons for evacuating the A/C system:

• The system was opened for service

• The system was opened by an accident or has been left

open

• It is unknown whether the system has been open

• Part of a leak check procedure

Refrigerant Recycling

A/C service stations automatically recycle the recovered

refrigerant during the evacuation process The refrigerant

is pumped continuously from the storage tank and passed

through the filter/dryer

Usually no special steps need to be taken as long as the

storage tank valves are open A sight glass and moisture

indicator will indicate the moisture content of the

refrigerant and the effectiveness of the filter/dryer

Replacing PAG Oil

Once the system has been evacuated and a deep vacuumexists, inject any required PAG oil Follow the procedurefor the machine you are using See the Repair Informationfor the specified type of oil

Do not attempt to add oil to a system that is pressurized.The pressure will blow oil out of its container Take carethat the oil supply container does not run out of oil If thisoccurs, air will be drawn into the A/C system and you willneed to evacuate again

Always keep oil containers tightly sealed PAG oil is scopic and absorbs moisture very readily Any containerleft open must be discarded and not used Whendisposing, PAG oil should NOT be added to waste engineoils

hygro-Notes:

A/C Refrigerant System Service & DiagnosisRecharging

A/C systems can be recharged by two methods:

• Pumping liquid refrigerant into the system high side with

A/C OFF

• Allowing the A/C compressor to draw refrigerant gas

into the low side with A/C ON

Most A/C service stations introduce liquid refrigerant on

the system high side Since the A/C compressor can be

damaged by liquid refrigerant, you must be sure that the

low side gauge hand valve is closed and the high side

hand valve is open when recharging This will allow

refrig-erant into the system high side only The refrigrefrig-erant will be

distributed throughout the system once the system is

started

The quantity of refrigerant to recharge is determined by

weight The specification is on a label in the engine

compartment and also in the Workshop Manual

Information

Be sure that the storage tank has sufficient refrigerant to

charge the system Modern A/C systems do not contain

much refrigerant so it is important to recharge the correct

amount To do this, the service station tank scale must be

accurate When recharging, be sure that the tank hoses

are not stretched and do not bump, move or touch the

machine or the storage tank

After the system is charged, turn the A/C ON with the

engine idling Be sure to close the service station high

side gauge hand valve before turning the A/C

system ON If this valve is left open, the refrigerant

storage tank will be exposed to high side pressures and

can explode

The A/C system should be ON continuously for at least

two minutes with the engine idling to properly distribute

the refrigerant oil

Performance test the system as described in this section

When system performance has been verified, remove the

service hoses Recover the refrigerant in the hoses per

the instructions and close the valves on the storage tank

and control panel

A/C System Performance Testing

An A/C system performance test should be performedbefore any service to verify a customer complaint of poorcooling performance It should also be performed to verifythat repairs have corrected the problem

Always be sure that the A/C system is mechanically OKbefore suspecting the electronics or controls A generalprocedure for performance testing the A/C systemincludes the following steps Always consult the RepairInformation for model-specific procedures and

specifications

• Close doors, windows, and sliding roof

• Insert temperature probe into center vent

• Measure ambient temperature

• Open all dash vents

• Switch ignition on

• Press recirculating air button

• Set temperature control to maximum cooling

• Switch fresh air blower to stage four

• Start engine

• Operate air conditioner while idling

• Set engine speed to 2000 RPM (start of time ment)

measure-Compare the outlet air temperature with specifications Ifthe specified temperature is not obtained, follow

diagnostic procedures in the service manual to determinethe cause

A/C Refrigerant System Service & Diagnosis

Importance of a Diagnostic Plan

A planned approach to the diagnosis of an A/C system

problem can help you to locate problems faster These

steps are typical:

• Perform a performance test

• Check the DTC memory

• Check pressure gauge readings

• Note unusual refrigerant line temperatures

• Verify correct quantity of refrigerant

• Test system components

The performance test will determine the nature of the

problem and verify the complaint Checking for stored

DTCs will identify suspect components or systems, and

whether the problem is likely to be electrical or

mechanical Pressure gauge readings will help to verify the

mechanical integrity of the A/C circuit

With A/C ON, high pressure lines and components should

be warm or hot Low pressure lines and components

should be cool or cold If a component is frosted or much

warmer or colder than normal, it could be plugged or

defective

If refrigerant charge quantity could cause the symptoms

noted, verify that the charge quantity is correct Test any

components that could cause the symptoms noted

Always follow procedures and use the specifications in the

Workshop Manual

Notes:

A/C Refrigerant System Service & DiagnosisDiagnosing with Pressure Gauges

The A/C compressor is a pump that creates high side and

low side system pressures The compressor pumps

against a restriction created by the expansion valve in

order to raise high side pressures Any mechanical fault in

the system that prevents the compressor from pumping

efficiently will result in pressures higher or lower than

desired The quantity of refrigerant also affects pressures

Checking high side and low side pressure can help to

diagnose poor A/C performance Remember that the

compressor’s job is to increase pressure on the high side

and reduce pressure on the low side Variable

displacement compressors can compensate for many

conditions and can make this diagnosis more difficult

Normal Pressures and Conditions

Normal A/C pressures will vary with changes in ture and humidity In general, as the temperature andhumidity increase, heat load and pressures also go up.Variable displacement compressors tend to keep low sidepressures relatively constant High side pressures go upand down with changes in heat load

tempera-The charts below show normal pressures for both displacement and variable displacement compressors

fixed-A/C Refrigerant System Service & Diagnosis

Leak Detection

A/C refrigerant leaks can be small and difficult to locate

Not all components are easily accessible and any

component in the refrigerant circuit can potentially leak

When checking for leaks, pay close attention to

connections, o-rings and seals

Electronic leak detectors can detect very small leaks for

both R-134a and R-12 refrigerants The detectors emit an

audible signal when refrigerant is sensed Refrigerant is

heavier than air, so always place the probe under the

component or connection when checking Evaporator

leaks can be checked by probing a low point, the

evaporator moisture drain

Electronic leak detector sensitivity can be affected if the

sensing tip is saturated with refrigerant or oil Fluorescent

dyes can be injected into the A/C system The dyes mix

with the system PAG oil and circulates with the oil Oil may

escape along with the leaking refrigerant and carry the

dye along with it An ultraviolet light (black light) causes

the dye to glow and can help to locate the leak

Warnings and Cautions

When servicing and repairing automotive climate controlsystems, you are exposed to several personal safetyhazards Be sure that you review and understand thesepotential hazards

Porsche Repair Information contains a list of safetyprecautions and warnings Read and understand thesewarnings and cautions before starting diagnosis or repairwork

Observe the following precautions:

• Automotive air conditioning systems and serviceequipment are under pressure and refrigerant can sprayunexpectedly Refrigerant temperatures may be veryhigh or low, creating the risk of burns or frostbite Besure to wear gloves and eye protection conforming toANSI standard Z87

• Never open a charged A/C system before recoveringthe refrigerant An operating A/C system can generatepressures up to 34.5 bar (500 psi)

• Work in a well ventilated area Refrigerants 12 and 134a both displace oxygen and are a suffocationhazard Refrigerants are heavier than air and can collect

R-in low areas with poor air circulation, such as under thevehicle

• Do not heat charged air conditioning systemcomponents to temperatures above 80° C (176° F).Pressure increases from high temperatures may causethe system to burst

• Store refrigerant containers at temperatures below 50° C (122° F) When charging an A/C system, do notheat containers with an open flame Use only warmwater to raise the temperature of refrigerant containers

• Before welding or soldering A/C components, recoverall refrigerant and flush the system with nitrogen Refrig-erants decompose with heat and produce corrosivesubstances A pungent odor indicates that thesesubstances are present Do not inhale They can causerespiratory problems

• Although refrigerant R-12 is not combustible, itproduces poisonous phosgene gas when burned Do

A/C Refrigerant System Service & Diagnosis

• R-134a is not normally combustible, but at pressures

above ambient and mixed with excess air, it can be

flammable Do not use compressed air to blow out A/C

refrigerant components or containers unless all of the

refrigerant has been recovered and the component has

been completely removed from the refrigerant circuit

• By law, containers used for recovered refrigerant may

be filled to 60% of capacity max

• Only use approved containers to recover refrigerant

• Secure refrigerant containers from falling Containers

can deform and burst or the valves can break off

• Do not steam clean A/C condensers or evaporators

The added heat can cause a dangerous increase in

refrigerant pressures

• The engine cooling system is pressurized Use care

when removing the pressure cap

• All current production Porsches use electric cooling

fans actuated by coolant temperature These fans will

come on at any time when coolant temperatures

exceed a certain value See Workshop Manual for

speci-fications

• For safety, most charging stations recharge A/C

systems by pumping the refrigerant into the system

with the compressor not running Make sure the high

side manifold gauge valve is always closed whenever

the compressor is running

Service Equipment Safety

• The hand valves on the manifold pressure gauges areopened to connect the red or blue Service Hoses andthe Manifold Center Port The Manifold Center Port isonly used when discharging, evacuating or rechargingthe system All other times, the hand valves are closed

• Fittings for R-134a service equipment are different fromthose used on R-12 systems This is to prevent cross-contamination of refrigerants Mixed refrigerants cannot

be reused and become hazardous waste that must bedisposed of properly

• R-134a service equipment uses quick connect fittings tominimize the discharge of refrigerant when connectingand disconnecting the hoses

• R-12 service equipment uses threaded fittings and handshut-off valves to contain refrigerant in the lines By law,the shut-off valves must be placed no more than 12inches from the ends of the service hoses to reducerefrigerant loss

A/C Refrigerant System Service & Diagnosis

First Aid

• If refrigerant contacts eyes or mucous membranes,

rinse immediately with large quantities of water and

seek medical attention

• If refrigerant contacts the skin, remove the wet clothing

and rinse immediately with large quantities of water

Seek medical attention if required

• If concentrated refrigerant vapor is inhaled, give the

person fresh air immediately Seek medical attention if

there is difficulty in breathing

Air Conditioning Basics

Air Conditioning Overview 2.3

Principles of Heat Transfer .2.3

The Refrigeration Cycle .2.7

Thermostatic Expansion Valve 2.13

Lines and Hoses 2.14

Service Connections 2.14

Refrigerants 2.15

Air Conditioning Basics

Notes:

Air Conditioning Basics Air Conditioning Overview

Air conditioning is the process of moving heat energy from

one place in the vehicle to another Doing this raises or

lowers the temperature of the air in the vehicle interior

The A/C system is a closed loop system in which a

refrig-erant is pumped by the compressor through the circuit

continuously While it is being pumped, the refrigerant

changes state from liquid to gas and back again The

refrigerant changes from liquid to gas in the evaporator as

it removes heat from the passenger compartment Then

the refrigerant gas condenses back to liquid in the

condenser, giving off heat to ambient (outside) air This is

a short description of how A/C works These concepts will

be discussed in more detail in the next section

Principles of Heat Transfer

There are four principles of heat and heat transfer thatapply to automotive heating, air conditioning and climatecontrol systems:

1 Heat always flows from hot to cold.

2 Materials absorb or give off large amounts of heat

when changing state

3 The pressure of a liquid or gas varies with its

tempera-ture and the temperatempera-ture of a liquid or gas varies withits pressure

4 The boiling point of a liquid varies with its pressure.

Air Conditioning Basics

1 Heat always flows from hot to cold.

Heat is a form of energy Cold is a term that means less

heat is present Cold materials contain less heat energy

than hot materials and heat always flows from the hotter

material to the colder

For example, if you hold an ice cube, your hand will feel

cold The ice removes heat from your hand and you sense

the loss of heat If you touch something warm, you feel the

heat flowing into your hand If a large amount of heat

transfers, you may be burned and feel pain

Practical Application

• Heat energy contained in the passenger compartment

air is absorbed by the cold refrigerant in the A/C

evapo-rator

• Hot refrigerant gives off heat and is cooled by cooler

ambient air flowing through the A/C condenser

In both cases, heat moves from hotter to cooler

Practical Application

• In the evaporator, liquid refrigerant boils attemperatures below the temperature of the air in thepassenger compartment The refrigerant absorbs largequantities of heat, far more heat than it would if itremained a liquid

• In the condenser, the reverse takes place Here, hotrefrigerant gas condenses back to liquid and gives offlarge amounts of heat to the cooler atmosphere Therefrigerant gives up far more heat than it would if itremained a gas

To explain, we need to look at two kinds of heat energy:

Sensible Heat and Latent Heat.

Sensible Heat – is measurable heat - a measurable

change in the temperature of a material Adding heatenergy raises the measurable temperature of a materialand increases Sensible Heat If we heat a pot of water on

a stove, the temperature of the water will increase and wecan measure this change with a thermometer (see illustra-tion, below)

Heat energy increasestemperature

of liquid

No change

of state

Air Conditioning BasicsLatent Heat – is heat energy that is added to a material

causing it to change state The temperature of the

material remains the same during the change of state We

can raise the temperature a pot of water to the boiling

point (100° C/212° F) by adding Sensible Heat energy, but

to make the water boil and change state from liquid to

gas, it takes much more heat energy in the form of Latent

Heat Similarly, when a gas condenses to a liquid, large

amounts of Latent Heat energy are released (see

illustra-tion, below)

The unit of heat energy is the BTU (British Thermal Unit)

One BTU = the amount of heat energy required to raise

the temperature of one pound of water one degree F At

sea level pressure, water boils at 212° F In order to raise

the temperature of one pound of water from 211° F to

212° F, only one BTU heat energy is needed But to

change that same pound of water at 212° F to one pound

of steam (gas) at 212° F requires 970 BTUs, a much

greater quantity of heat When the water condenses back

to a liquid, it gives off the same 970 BTUs of heat

In the A/C system, refrigerant evaporates and condenses

over and over as it is pumped through the system R-134a

refrigerant absorbs or gives off large amounts of latent

heat energy (about 85 BTU/lb) as it changes state This is

the key to the efficiency of A/C systems

3 The pressure of a liquid or gas varies with its temperature and the temperature of a liquid or gas varies with its pressure.

The pressure of the refrigerant in the closed A/C circuitwill vary with changes in temperature, and the temperature

of the refrigerant varies with changes in its pressure WithA/C off and at an ambient temperature of 21° C (70° F),the pressure in a fully charged system will be approxi-mately 4.8 bar (70 psi)

As the temperature rises, the pressure will also rise Thetable below shows the temperature/pressure relationshipfor R-134a at temperatures between -30° C (-22° F) and70° C (158° F)

At -30° C (-22° F) refrigerant pressure drops to 0 bar (0psi) At this temperature, liquid refrigerant in an opencontainer will not boil and will remain a liquid

Practical Application

• The job of the A/C compressor is to compressrefrigerant gas, raising its pressure and temperatureand concentrating the heat The refrigerant flows to thecondenser where it is much hotter than the ambient airblowing through and gives up latent heat to the air

• In the evaporator, refrigerant is exposed to lowpressure This lowers its temperature and the coldrefrigerant absorbs latent heat from the passengercompartment

Note:

The temperatures of the A/C lines when the A/C is ON.The high pressure lines will be warm or hot, the lowpressure lines will be cool or cold

R-134a Refrigerant Pressure vs Temperature

Latent Heat

Air Conditioning Basics

4 The boiling point of a liquid varies with its

pressure.

The boiling point of a liquid changes with pressure For

example, engine coolant temperatures can easily climb

above the boiling point of the coolant/water mixture at sea

level pressure, about 108° C (226° F) By increasing the

pressure to 1 bar (15 psi) the boiling point is raised to

128° C (263° F)

Practical Application

• When the A/C system is operating, the refrigerant

pressure in the evaporator is low which lowers its

boiling point This allows the liquid refrigerant to boil

and to change state to a gas, absorbing latent heat

• In the condenser, the pressure of the refrigerant gas is

high, raising the boiling point and allowing it to

condense to liquid as heat is removed

R-134a refrigerant is as a gas at atmospheric pressures

and ambient temperatures In the closed refrigerant

circuit, some refrigerant is in liquid form because of the

higher pressure As with water, the boiling point of

refrig-erant increases as its pressure increases

Reducing pressure to below-atmospheric (partial vacuum)

lowers the boiling point of a liquid The table shows the

boiling point of water at several low pressures The value

29.92 in Hg is atmospheric pressure at sea level At this

pressure, the boiling point of water is 100° C (212° F) At

higher altitudes, such as in Denver, the pressure is lower,and therefore the boiling point is lower This is why baking

or cooking times are longer at high altitudes

On the table, note the low pressure at which water will boil

at room temperature (shown in bold) This low pressure isattained during refrigerant system evacuation At this lowpressure, any water present in the A/C system will boil off

Notes:

Air Conditioning Basics

The Refrigeration Cycle

As we have said, air conditioning is the process of moving

heat energy from one place in the vehicle to another The

A/C system is a closed system in which the compressor

pumps the refrigerant through the circuit over and over

whenever the A/C is ON

While it is being pumped, the refrigerant changes state

from liquid to gas and back again The refrigerant changes

from liquid to gas in the evaporator as it removes heat

from the passenger compartment Then the refrigerant

gas condenses back to liquid in the condenser, giving up

heat to ambient (outside) air The refrigerant does not get

worn out or used up unless there is a mechanical problem

or a leak

The amount of heat moved from inside to outside the

vehicle determines the heat load Both temperature and

humidity affect the heat load The refrigerant circulates in

the closed circuit made up of these components:

• Regulation and Control Devices

High and Low Pressure Sections

The system is divided into high pressure and low pressuresections They are the "high side" or discharge (D), and

"low side" or Suction (S) The compressor is the pump thatraises refrigerant pressure on the high side of the systemand reduces pressure on the low side

• The compressor and the expansion valve separate thetwo sides of the system

• The condenser and receiver dryer are always on thesystem high side

• The evaporator is always on the system low side

Notes:

Air Conditioning Basics

Compressor

The compressor is an engine-driven refrigerant pump It

compresses the refrigerant gas to raise both temperature

and pressure The compressor also moves refrigerant

through the system

All Porsche Sports Cars and Cayenne A/C compressors

are variable displacement swash plate designs Fixed

displacement compressors were used on 911 Carrera

(993) and earlier models

The compressor is belt driven On Sports Cars an

electro-magnetic clutch is built into the compressor pulley to

engage and disengage the drive On Cayenne, there is no

clutch The compressor shaft turns at all times with the

engine When no A/C is desired, compressor displacement

can be reduced to nearly 0%

Compressor piston downstroke draws in low pressure

refrigerant gas from the evaporator On the upstroke, the

refrigerant is compressed, raising both pressure and

temperature Refrigerant pressure increases from approx

0.6-1.7 bar (9-25 psi) to approx 6-25 bar (87-363 psi)

The compressed refrigerant gas is pushed out of the

compressor to the condenser The compressor can raise

the pressure of the refrigerant because it is pumping

against a restriction created by the expansion valve The

system high side contains high pressure refrigerant, and

includes the compressor outlet, condenser, receiver-dryer

Reed valves are flat plates of spring material located in thecylinder head above each piston They bend one way onlyand allow flow in one direction They open and close auto-matically in response to pressure changes as the pistonstravel up and down

The reeds are designed to pump refrigerant gas only, andthe compressor pistons have little clearance at the top oftheir stroke Liquid refrigerant must be kept out of thecompressor as it can hydraulic lock and damage it

Fixed Displacement Compressors

Fixed displacement compressors have a fixed pistonstroke and always pump the same volume of refrigerantfor each revolution of the compressor shaft The pistonstroke never varies and the compressor's displacementnever changes

All A/C compressors must have sufficient capacity forgood cooling under high heat load conditions and lowengine speeds Since fixed displacement compressorscannot vary the amount that they pump, under conditionswith high engine speed and low heat demands, thesecompressors have much greater capacity than is required.Energy can be wasted pumping this excess refrigerant.Also, the compressor clutch may cycle ON and OFF morefrequently than is desired

Notes:

Air Conditioning BasicsVariable Displacement Compressors

Porsche vehicles today use a variable displacement

compressor Seven axial pistons are arranged

concentrically around the central compressor shaft A

smooth disk is attached to the compressor shaft Slipper

shoes follow the disk's oscillating motion and the angle of

the disk transmits reciprocating forces to the pistons

Variable displacement compressors can vary the piston

stroke and can change output volume The longer the

piston stroke, the greater the displacement and output

The stroke is determined by the angle of the swash plate

on the compressor shaft Variable displacement

compres-sors change the swash plate angle to match the

refrigerant flow rate to the heat load on the system

Sports Cars – Variable Displacement Compressor,

Low Displacement Position

Sports Cars – Variable Displacement Compressor,

High Displacement Position

Variable displacement compressors are more efficientthan fixed displacement compressors because they pumponly enough refrigerant to achieve the desired cooling.Energy is not wasted pumping more refrigerant than isnecessary Also, clutch cycling is eliminated and engineidling is improved with variable displacement

Low Heat Load - 5% Output

The conditions are met when engine r.p.m is consistentlyhigh, e.g expressway driving, and/or temperature is low.The suction pressure is relatively low and the control valve

is open The angle of the rotating disk is at its lowest and

so delivery is at its minimum

High Heat Load - 100% Output

The conditions are met when engine r.p.m is consistentlylow and/or temperature is high The suction pressure ishigh and closes the control valve The angle of the rotatingdisk is at its greatest and so delivery is at its maximum

Notes:

Air Conditioning Basics

Mechanical Regulating Valve

Porsche Sports Cars up to MY 2008 use variable

displace-ment compressors with mechanical regulating valves

Cayenne MY 2003 - on and Sports Cars as of MY 2009

have a variable displacement compressor controlled by a

PWM electronic control valve Both types regulate

compressor displacement by changing pressure in the

crankcase under the pistons

Pressure Relief Valve

Porsche A/C compressors have a spring loaded

mechan-ical pressure relief valve If system pressures get

danger-ously high, the valve will open and vent the excess

pressure The valve closes when pressures have dropped

to safe levels to prevent the complete loss of refrigerant

Opening pressure is approximately 38 bar (550 psi) The

Lubrication

All A/C compressors require oil for lubrication The oilreduces internal friction and heat and helps to seal movingparts This lubricant is carried by the flow of refrigerantthroughout the system and it must be compatible with therefrigerant, seals and components

Porsche A/C systems with R-134a refrigerant usesynthetic PAG (polyalkylene glycol) or ester oil R-12systems use mineral oil These oils are not compatible.Mineral oil will not mix with R-134a refrigerant and mustnot be used in R-134a systems Since the oil flows withthe refrigerant throughout the system, a portion of thetotal oil charge must be replaced when any component isreplaced Some oil may also be removed along with therefrigerant when discharging a system

A/C service stations have provisions for capturing andmeasuring any oil removed so that an equal amount can

be restored A typical system contains approx 195 cm3(6.6 oz.) of ND8 PAG oil Refer to Service Information forspecifications regarding the amount of oil to add for eachsystem component

Caution:

• Always store refrigerant oil in closed containers Theseoils are very hygroscopic, that is, they readily absorb

Air Conditioning BasicsCondenser

The condenser is a heat exchanger located in the front of

the vehicle It is similar to the engine radiator and has a

large surface area for efficient heat transfer Some

Porsche models use two condensers The condenser is on

the A/C system high side and contains high pressure

refrigerant

The condenser allows high pressure, hot refrigerant gas to

give off heat energy to cooler air passing through the

condenser fins Forward motion of the vehicle and electric

fans both promote this air flow

The refrigerant changes state in the condenser in this

sequence:

• High pressure refrigerant enters the condenser as a hot

gas: 60-100° C (140-212° F)

• The heat energy that was absorbed by the refrigerant in

the evaporator is transferred to the cooler ambient air

passing over the condenser's tubes and fins

• The refrigerant gas gives up both sensible heat and

large amounts of latent heat energy to the cooler

ambient air

• The gas cools, changes state and condenses to a

liquid

• The refrigerant leaves the condenser as a very warm

high pressure liquid

The DME controls system cooling fans based on engine

load When the A/C is ON, the electric cooling fan comes

ON to improve airflow and heat transfer

Receiver/Dryer

911 Carrera (996) Receiver/Dryer

The receiver/dryer is a reservoir for refrigerant on thesystem high pressure side It is located between thecondenser outlet and evaporator inlet Condensed liquidrefrigerant flows into the receiver dryer from thecondenser

As heat load on the A/C system changes, more or lessrefrigerant will be in the liquid state Also, over time, somerefrigerant will escape past seals The receiver/dryer acts

as a reservoir for refrigerant to compensate for theseconditions The pickup tube in the receiver/dryer ensuresthat only liquid refrigerant is sent to the expansion valve.The receiver/dryer contains a desiccant to removemoisture from the system The desiccant can absorb 6-12

g of water This is not much, and moisture must be keptout of the system during repairs

R-12 systems included a sight glass on top of thereceiver/dryer The flow of liquid refrigerant could be seenthrough the glass and a stream of bubbles indicated lowrefrigerant level A sight glass was used on some R-134asystems in the early 1990’s A/C service equipment accu-rately measures the refrigerant charge by weight, makingthe sight glass unnecessary

When retrofitting an R-12 system with R-134a, alwaysreplace the receiver/dryer as R-12 desiccants are notcompatible with R-134a, and the desiccant will be perma-nently saturated with mineral oil

Air Conditioning Basics

Evaporator

The evaporator is a heat exchanger located in air

distribu-tion housing It has tubes and fins similar to a radiator or

condenser and it has a large surface area for efficient heat

transfer The evaporator permits cold refrigerant to

absorb heat from warm air in the passenger

compartment Outside air or recirculated air is forced

through the air distribution housing and evaporator fins by

blowers

The evaporator is on the A/C system low pressure side

The thermostatic expansion valve (TEV) is a restriction

controlling how much refrigerant enters the evaporator

The refrigerant changes state in the evaporator in this

sequence:

• Liquid high pressure refrigerant sprays into the

evapo-rator, controlled by the TEV orifice

• The pressure of the refrigerant drops as it passes

through this orifice At this low pressure, the refrigerant

temperature is above its boiling point The refrigerant

boils rapidly and changes state

• As the refrigerant becomes a gas, it absorbs both

sensible heat and large amounts of latent heat from the

cabin air passing through the evaporator fins

• The refrigerant warms and the cabin air passing over

the evaporator fins cools

In addition to removing heat, the evaporator also fies the interior air Cool air cannot hold as much moisture

dehumidi-as warm air As the air is cooled, moisture condenses andcollects on the evaporator fins Dehumidifying the air adds

to passenger comfort and also helps to demist the shield in damp weather This is why A/C is enabled whenthe defrost function is selected

wind-Evaporator fin temperatures cannot be allowed to dropbelow the freezing point of water, 0° C (32° F), or thecondensation can freeze and ice buildup can block theevaporator fins Dust and matter carried in with theairstream tends to collect on the wet evaporator fins, sothere is a cleaning effect The condensed water thatcollects on the evaporator fins is allowed to drain

Notes:

Air Conditioning BasicsThermostatic Expansion Valve (TEV)

The Thermostatic Expansion Valve (TEV) is located at the

evaporator inlet It separates the high and low pressure

sides of the system and creates the restriction that the

compressor uses to build high side pressure High

pressure liquid refrigerant flows to the expansion valve

inlet from the receiver/dryer

Porsche uses the H-Type block expansion valve This valve

works the same way as the old style right-angle valve with

external sensing tubes, but is internally compensated

within the valve and has no external lines to the

evaporator

The TEV has a variable orifice which controls the amount

of refrigerant admitted into the evaporator High pressure

liquid refrigerant passes through the TEV orifice at the

evaporator inlet The liquid refrigerant sprays into the

evaporator where it is exposed to low pressure and rapidly

evaporates The TEV senses both temperature and

pressure in the evaporator Both evaporator inlet and

outlet lines pass through the TEV Refrigerant temperature

is sensed at the evaporator outlet Increases in evaporator

outlet gas temperature due to increased heat load cause

the diaphragm in the gas filled thermostatic valve element

to move downward, opening the ball valve a greater

amount against spring tension and admitting more

refrig-erant

The expansion valve also senses evaporator inlet

pressure Pressure acts on the underside of the

diaphragm in the gas filled thermostatic valve element

Any decrease in evaporator pressure tends to open the

ball valve and increase the amount of refrigerant admitted

This would be the case if the evaporator were "starved"

and required more refrigerant When additional refrigerant

flows into the evaporator, more refrigerant is available to

absorb heat This reduces the temperature at the

evaporator outlet, causing a pressure drop in the

thermo-static valve element and increases evaporator pressure

Both conditions act on the diaphragm to reduce the ball

valve opening The cross-section opening of the valve is

reduced as the spring pushes the ball valve toward its

seat

Notes:

Air Conditioning Basics

Lines and Hoses

A/C system components are connected by rigid lines and

flexible hoses This creates the closed loop through which

the refrigerant flows Rigid lines are formed aluminum The

flexible hoses are a reinforced rubber compound with a

barrier liner

Low pressure lines and hoses are generally larger in

diameter when compared with high pressure lines and

hoses This is because refrigerant gas in the low side has

expanded and takes up much more space than either

refrigerant gas or liquid on the high side

Joints may be several types but always have o-rings for

sealing When assembling lines or replacing o-ring seals,

always lubricate o-rings only with PAG oil The oil helps the

o-ring to properly seat and seal Do not use any other

lubricant Always torque fasteners to specifications

Service Connections

911 Carrera (993) models have A/C high and low side

service connections located in the rear near the A/C

compressor

911 Carrera (996)/(997) and Boxster (986)/(987) model

connec-tions are located in the cowl area on the right side, near the

battery and expansion valve.

Cayenne model service connections are in front in the engine compartment on the left side.

R-134a service connection fittings are quick-connect styleand are different from those on R-12 systems This wasdone to prevent cross-contamination of refrigerants whichcannot be mixed R-134a quick connect fittings aredifferent sizes for the high and low sides This ensuresthat the low side and high side service hoses are properlyconnected to their respective ports Disconnecting an R-134a service hose quick-connector automatically seals theports to retain the refrigerant in the vehicle’s system andalso in the service hose

R-12 systems use threaded service connection fittings andhand shut-off valves By law, the shut-off valves must be nomore than 30 cm (12 in.) from the end of the service hose

to reduce refrigerant loss

Air Conditioning BasicsRefrigerants

The refrigerant is the substance that is pumped by the

compressor through the closed system to transport heat

from one place to another The refrigerant changes state

from a liquid to a gas and back again as it cycles It does

not wear out or get used up unless it gets contaminated

Refrigerant R-12 (Dichlorodifluoromethane, trade name

FREON) was the refrigerant used in vehicles for decades

R-12 was considered completely inert, safe and harmless,

but it is a CFC or Chlorofluorocarbon CFCs contains

Chlorine which is suspected of damaging the ozone layer

and contributing to global warming

R-12 is no longer produced in this country, and

Porsche discontinued its use in 1993.

R-134a (Tetrafluoroethane, trade name SUVA) is the

refrig-erant used today It has similar heat transfer properties

like R-12 but it does not contain Chlorine R-134a has 84%

less global warming potential than R-12 and it does not

destroy ozone For these reasons, R-134a has been

judged to be better for the environment R-134a is the only

approved refrigerant and the only approved replacement

for R-12

R-134a and R-12 refrigerants are not compatible and will

not mix Cross-contamination must be avoided when

servicing the A/C system To reduce the possibility of

errors, refrigerant storage containers are different colors

(white for R-12 and light blue for R-134a), and fittings are

different Mixed refrigerants are a hazardous waste that

must be disposed of properly

As mentioned before, the lubricating oils are different for

each refrigerant R-12 systems use mineral oil and R-134a

systems use synthetic PAG or ester oils

Note:

Refer to Equipment Bulletins for recomendation of a

refrig-erant tester that can analyze the refrigrefrig-erant used in a

vehicle

Notes:

Air Conditioning Basics

Notes:

Sports Cars Systems

Sports Cars Systems – 9x6 & 9x7

A/C Systems General Information 3.3

System 1 Description – Boxster (986) & 911 (996)

Refrigerant System Description .3.4

Air Distribution System 3.5

Regulating Air Temperature 3.6

Control Panel Function, 911 Carrera (996) & Boxster (986) 3.8

Sensors and Actuators 3.10

Sensors .3.12

Actuators .3.14

Service and Diagnosis Information .3.16

On Board Diagnostics .3.17

System 2 Description – Boxster/Cayman (987) & 911 (997) up to 2008, 911 Turbo up to 2009

Manual Air Conditioning, Boxster/Cayman (987) 3.18

Automatic Climate Control, 911 Carrera/S (997) Optional Boxster/Cayman (987) 3.20

Interior Sensor 3.22

Cooling Fans 3.22

Service and Diagnosis Information .3.24

Information Transmitted Via CAN Interface 3.24

System 3 Description – Boxster/Cayman (987) & 911 (997) as of 2009 (except 911 Turbo)

Externally Controlled Compressor 3.25

Sports Cars Systems

Notes:

Sports Cars Systems Sports Cars 9x6 & 9x7 A/C Systems

General – Boxster (986) & 911 (996)

The automatic climate control system automatically

maintains the selected passenger compartment

tempera-ture The system is capable of maintaining temperatures

between 18-29° C (64-84° F), with 22° C (72° F)

recommended In automatic operation, the system

deter-mines and controls blower speed, outlet air temperature,

and outlet selection The automatic climate control system

also permits manual selection of temperature and air

distribution if desired

General – Boxster (987) MY 2005 - 2008

Cayman (987) MY 2006 - 2008

The Boxster/Cayman (987) series feature manual air

conditioning with combined interior filter (active carbon

and pollen filter) as standard equipment Automatic climate

control is available as an option

Both systems; air conditioning and automatic climate

control are further developments of the respective

previous systems They have been revised to ensure more

even and more comfortable ventilation of the passenger

area and to improve the user friendliness of all air

The advantages of the new air conditioning systems:

• Ensures more even ventilation of the passenger area

• Is considerably less prone to drafts

• Is quieter

• and offers increased functionality

The air conditioning system employs a CFC-freerefrigerant In order to ensure an adequate supply of elec-trical energy (taking additional facilities into consideration),the 70 Ah battery is more powerful than its predecessorand has been weight optimized

General – 911 Carrera/S (997) MY 2009

The 911 Carrera (997) series are the first sports cars tofeature the “externally controlled compressor” system.With an externally controlled system, the air conditioningoperating panel has a direct effect on the compressor andthus on the cooling output Given this, most changes hererelate to the compressor or compressor control The com-ponents, which you will be familiar with from the air-condi-tioning system used in the previous model, are not modi-fied to any great extent by this system and are essentiallyidentical from the point of view of design and operatingprinciple A comparable externally controlled compressorsystem is also used in the Cayenne

Advantages of an externally controlled compressor:

• Reduced weight due to removal of a compressor clutch– Total weight loss here: approx 3 lbs (1.4 kg)

• No need to push the clutch when engaging fort use)

(high-com-• Refrigerant output is controlled more precisely and isdemand-controlled, based directly on the evaporatortemperature

Sports Cars System 1 (9x6)

Sports Cars 9x6 A/C System Description

– Boxster (986) & 911 (996)

Compressor

The A/C compressor is a continuously variable 7-cylinder

swash plate design An internal mechanical regulating

valve varies compressor displacement by changing

pressure in the crankcase under the pistons The

regulating valve senses changes in refrigerant high side

and low side pressures These pressures are an indication

of heat load: high displacement for high heat load, low

displacement for low heat load The compressor

displace-ment is 160 cm3(9.8 in 3) at 100% output Output can be

as low as approx 5%

Condensers

Two A/C condensers are used on the Boxster (986) and

911 (996) models They are mounted in the front of thevehicle on the left and right-hand sides in front of theengine coolant radiators Each condenser is cooled by theelectric cooling fan to ensure sufficient airflow and heattransfer under all driving conditions Refrigerant flowsthrough the right side condenser first, then the left

Receiver Drier

The refrigerant tank is installed in the fresh air chamber atfront left, next to the battery The pressure relief valve (seearrow) for the refrigerant system is also located here

Sports Cars System 1 (9x6)Evaporator

The A/C evaporator is located in the air distribution

housing Evaporator removal requires removal and

disas-sembly of the air distribution housing

Thermostatic Expansion Valve (TEV)

The H-Type block Thermostatic Expansion Valve (TEV) is

located at the evaporator inlet in the cowl area on the right

side of the battery

Service Connections

Service connections are located in the cowl area on the

right side, near the battery and expansion valve

Notes:

Air Distribution System

The air distribution system controls air volume,temperature and direction within the passenger compart-ment The system can add or remove heat from the cabinair and provide ventilation, heating, cooling and defrostfunctions

On Boxster (986) and 911 (996) models, the water cooledengine allows the use of a heater core with hot enginecoolant to add heat to the interior The air distributionhousing contains the evaporator, heater core, blower fan,air control flaps and their actuators, and passages tovarious air outlets in the vehicle

The air distribution housing mixes fresh (outside) air, culated air, cooled air and heated air to obtain the desiredinterior temperature A blower distributes this air to thesystem outlets

recir-Air and Flap Controls (heater box)

1 - Fresh air intake port

2 - Fan motor

3 - Fan regulator / output stage

4 - Central distributor flap

5 - Heat exchanger

6 - Evaporator

7 - Expansion valve (on rear side)

Sports Cars System 1 (9x6)

Recommended air distribution:

1 - Fresh air intake port

2 - Distributor flap for fresh air/recirc air

3 - Recirculating air intake port

4 - Fan motor

5 - Evaporator

6 - Temperature mix flap

7 - Heat exchanger

8 - Defrost air outlet vent

9 - Footwell/defrost distributor flap

10 - Footwell air outlet vent

11 - Central distributor flap

12 - Central and side vents

In summer – Air distribution to central and side vents

In winter – Air distribution to the footwell and the front

windshield

Back Pressure Compensation

The air throughput is influenced by the back pressure

which arises in the area of the fresh air inlet according to

the vehicle speed In order to compensate for this

depen-dency, the distributor flap for fresh air/recirculated air

(back pressure flap) is moved in the direction of “closed”

(recirculated air) according to the vehicle speed (from 55

mph/90 km/h) The flap setting is also dependent on the

fan voltage

Regulating Air Temperature

The air distribution housing is attached to the bulkheadunder the instrument panel The housing includes the evap-orator, heater core, blower, air control flaps and

actuators, ducts and outlets

Fresh air enters the intake duct in front of the windshield.All air entering the air distribution housing first passesthrough the evaporator where, with A/C ON, the air iscooled more than desired and dehumidified by the coldevaporator