CH53 heating and air conditioning service STUDENT VERSION re

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Chapter 53

Air-Conditioning Diagnosis and Service

Service Precautions

• Wipe away any oil or dirt before disconnecting a connection

• Keep tools clean and dry

• Refrigerant oil containers must be clean and dry

• Leave a system open for the shortest time

possible

• Evacuate a system any time it has been opened

Refrigerant Safety Precautions

• Work in a well-ventilated area

• Refrigerant will cause frostbite if it contacts exposed skin or eyes

• Wear protective gloves and clothing in

addition to eye protection

• Never use compressed air to leak test a R-134a system

Refrigerant Safety Precautions

• Never drop, strike, puncture, or burn a

refrigerant container

• Never expose A/C systems or refrigerants

to high temperatures or open flame

• Never overfill refrigerant containers

• Never mix R-12 and R-134a, components,

or equipment

Special Precautions for Hybrid Vehicles

• The A/C is usually powered by the

high-voltage system

• Follow all precautions and service

procedures given by the manufacturer

• Ensure the use of the correct refrigerant oil

Initial System Checks

• Verify the complaint

• Check operation at full heat and full cold

• Pay attention to smells and noises

• Inspect the compressor drive belt

• Look for a film of oil leakage

• Check for condenser airflow restrictions

• Expansion valve should be frost free.

• Check the sight glass if equipped

Trouble Codes

• May have

self-diagnostic capability.

• Automatic climate

controls are very

likely to have codes

and data.

– Moldy or musty smells

– Cabin air filters

Purity Test

• Performed when the contents of the system are unknown

• A refrigerant identifier samples contents

• Can prevent damage to equipment and

injury in the event combustible agents are present

Manifold Pressure Gauge

Connecting the Gauge Set

• Locate the high- and low-side service

valves

• Make sure the gauge set valves are closed

• Purge each gauge set hose to remove air trapped in the hoses and gauges

Testing Procedures

• Run engine between 1500 and 2000 rpm

• Close all vehicle windows and doors

• Set A/C to maximum cooling

• Check gauge pressures and outlet

temperature

• Refer to the manufacturers temperature and pressure charts

Performance Testing Readings

• High-side pressure is

higher than normal:

– Air in the system

– Restriction on the high

side

– Poor airflow across the

condenser

• High-side pressure is lower than normal:

– Low refrigerant – Defective compressor

Performance Testing (cont’d)

– Faulty metering device – Poor airflow across the evaporator

– Restriction in the low side

– Refrigerant undercharge

Leak Testing

• Leaks often cause low pressure readings

• Perform a visual inspection

• Leak detectors:

– Electronic leak detector

– Fluorescent (UV) leak tracer

– Fluid leak detector

• Most manufacturers do not recommend stop leak products

Electronic Leak Detector

Fluid Leak Detection

Emptying the System

• Identify the refrigerant

• Follow the equipment

manufacturer’s

procedures

• Recover until gauges

show vacuum

General Service

• All refrigerant must be recovered

• Component replacement may require the addition of refrigerant oil to system

• Use the specific type and quantity oil

required

• Too much oil reduces cooling capacity

• Too little oil results in poor lubrication

Clutch Service

• Inspect for discoloration, peeling, or other damage

• Check pulley drag and play

• Measure clutch coil resistance

• Inspect clutch clearance with a feeler gauge

• Some clutches can be replaced on the

vehicle

System Flushing

• Compressor failure causes foreign material

to pass into the system

• Flush the condenser and lines

• Replace the accumulator/dryer

• Use only the flushing agent specified by the manufacturer

In-Line Filters

• Most effective way to trap debris

• Install whenever a compressor has seized or had severe damage

• Filters without orifices should be installed

in the liquid line between the condenser and evaporator

– Pressure cycling switch

– Low-pressure cutoff switch

– Electronic cycling control switch

– High-pressure cutoff switch

– Evaporator temperature sensor

Hoses and Fittings

• Total hose replacement is the preferred

method to correct a hose leak

• Inspect fittings

• Spring lock fittings require special tools

• Lubricate new O-rings with refrigerant oil

Receiver/Dryer and Accumulator

• Should be changed when there has been a leak and/or component replacement

• The desiccant rapidly draws moisture and can be contaminated in less than 5 minutes

• Keep new unit sealed until ready to install

• Some can be replaced from under the hood

or under the dash

• Many require dash removal to replace

• Inspect the evaporator drain:

– Inadequate or no draining will allow water to back up into the evaporator case

– Can cause wet floorboards and mildew smells

Evaporator Controls

• Newer models use

orifice tubes

• Insert removal tool

and remove tube

• Coat new tube with

clean refrigerant oil

Recharging the System

• Evacuate the system to remove all trapped air and moisture

• The vacuum pump should remain connected for at least 30 minutes after 26 to 29 inches

of mercury is reached

Charging Cylinder

• To accurately measure charging by cylinder weight, it is necessary to compensate for

variations caused by temperature

• A calibrated chart is used based on tank

pressure

Climate Control Systems

• Most systems have self-diagnostics

• Inspect blower motor operation

• Check operation of controls, doors and ducts

• Solar sensor operation may be checked through scan data