CH52 heating and air conditioning STUDENT VERSION rev

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Chapter 52

Heating and Air-Conditioning

• The interior fan circulates air within

compartment when the vehicle is stopped

Automotive Heating Systems

• Works with the engine’s cooling system

• Heat is used from the circulating coolant

• All vehicles must have passenger

compartment heating and windshield

defrosting

Heater System Service

• Many times heating system problems are

also cooling system problems

• Inspect coolant level and condition

• Check temperature of heater inlet and outlet hoses

• Check heater control valve for sticking

open/closed and the valve’s controls

Blower Motor Service

• Check power and

Heater and Defroster Duct Service

• If the blower runs but no air comes out,

inspect airflow control or blend door

• Blend and vent selection controls can be

cable, vacuum, or electrically controlled

Theory of Air-Conditioning

• Heat Flow

– All substances contain heat.

– Heat always flows from a warmer object to a colder one.

– The greater the temperature difference, the greater the rate of heat flow.

– The amount of heat necessary to change the

state of a substance is called latent heat.

Theory of Air-Conditioning

(cont’d)

• Pressure and Boiling Points

– Changing pressure on a substance changes its boiling point.

– The greater the pressure, the higher the boiling point.

– If pressure is raised on a vapor, the vapor

condenses at a higher temperature.

• Moves the heat from one point to another

• Before 1994 R-12 was used

• A hydrofluorocarbon (HFC)

• Less damaging to the ozone layer

• Not interchangeable with R-12

• R-134a operates at higher pressures

• European and Japanese manufacturers are

to phase out R-134a by 2011

Alternative Refrigerants

• The EPA list of approved alternatives

• Flammable substances are illegal

Basic A/C System Operation

• As the refrigerant changes state, it absorbs heat

• If the refrigerant pressure is high so is it’s

Basic Refrigerant Cycle

Refrigerant Oils

• Mixed with the refrigerant

• R-12 systems used mineral oil

• R-134a systems require polyalkeline glycol (PAG) or polyester (POE) oils

• Hybrid electric A/C systems require special non-conductive oils

• Transfers heat from the refrigerant to the outside air

• Mounted in front of radiator

• Condenses or liquefies the high-pressure high-temperature vapor

• Connected on the high

side of the system

• Used on older systems

• Stores any liquid

refrigerant that flows

out of the evaporator

Thermostatic Expansion Valve

• Flow to the evaporator must be controlled

• The TEV is mounted at the evaporator inlet and separates the high side from the low

side

• Regulates flow by balancing inlet flow and outlet temperature

• Receives atomized refrigerant spray

• Acts as a boiler or vaporizer

• As the refrigerant boils it absorbs heat

• Moisture in the air condenses on the outside

of the evaporator and is drained off

Service Fittings

• R-12

• R-134a

A/C Systems and Controls

• Cycling Clutch Systems

– Compressor runs intermittently

• Evaporator Pressure/Temperature Control Systems

– Compressor operates continuously when A/C controls are in the on position

• High-pressure relief valve

• Compressor control valve

• Electronic cycling clutch switch

Manual/Semiautomatic Controls

• Operate similar to heater controls

• Control head settings control blend door and air direction

• Cooling controlled by control settings and blower speeds

Automatic Climate Control

• Maintains specific

temperature

• Uses heat sensors

• A control module uses

sensor and driver input

to control the

compressor and blend

functions

Typical A/C-Heater Ducts

Dual Zone Systems

• Both driver and passenger sides have separate climate controls

• Some systems are tied into the navigation