A/C System Component Overview
Compressor
The compressor is driven via a belt on the engine when the A/C clutch engages (A/C "ON").
Low-pressure refrigerant gas from the evaporator is compressed by the compressor. After compression, the refrigerant gas (now high-pressure) flows to the condenser.
NOTE:
- The compressor contains refrigerant oil that is mixable under all temperatures with the refrigerant
- A label on the compressor indicates that compressor is for R-134a systems only.
Condenser
The condenser transfers heat from the compressed refrigerant gas to the outside air which causes the refrigerant to change state from a gas to a liquid.
NOTE: The condenser for the R-134a refrigerant system is identified with a green label.
Receiver Drier
The receiver drier acts as a refrigerant reservoir for the system. Any moisture in the system is absorbed in the drier desiccant.
CAUTION!
The receiver drier may be identified with a green R-134a label and MUST NOT be used in R-12 systems (the drier desiccant inside is only compatible with R-134a refrigerant). Likewise, NEVER use an R-12 receiver drier in and R-134a system.
Sight Glass (if equipped)
With a properly charged A/C system and A/C clutch engaged, the sight glass - arrow- should remain clear and bubble free.
NOTE:
- The mixture of R-134a refrigerant and refrigerant (PAG) oil may appear milky in the sight glass.
- If equipped, sight glass location may not be as illustrated.
Expansion Valve
The expansion valve restricts and controls refrigerant flow to the evaporator thus lowering refrigerant temperature and pressure.
NOTE: The R-134a expansion valve may be identified with a green label.
Evaporator
Liquid refrigerant entering the evaporator absorbs heat from air passing through the evaporator fins and cools the air. As the refrigerant absorbs heat it turns to vapor and then is suctioned by the compressor.
O-Rings
O-rings seal connections between A/C system components.
NOTE:
- Always use correct size O-rings (dimensions -a- and -b-).
- Do not reuse O-rings, always replace. Use only new O-rings that are compatible with R-134a refrigerant and refrigerant (PAG) oil on R-134a systems.
- O-rings for use only on R-134a systems may be color coded: red, green, violet or black.
- Lubricate O-rings with the appropriate refrigerant oil before installing (only use PAG oil).
Pressure Relief Valve
The pressure relief valve is mounted on the compressor or compressor inlet/outlet manifold. At pressures above 40 bar (580 psi), the pressure relief valve opens to vent excessive pressure. When the system pressure is reduced, the valve closes to prevent total refrigerant loss.
On some models, a cap on the pressure relief valve will pop out if the valve has opened.
A/C Pressure Switch -F129-
NOTE: Depending on engine type, refrigerant systems have either an A/C pressure switch -F129- or high pressure sensor -G65- installed. Refer to appropriate wiring diagram.
Switch -F129- has three functions:
- Switches the A/C clutch -N25- off when excessive refrigerant circuit pressure is present (e.g.: insufficient air flow over condensor or when overcharged).
- Switches the A/C clutch -N25- off when insufficient refrigerant circuit pressure is present (e.g.: when refrigerant has leaked out)
- Switches on the second speed coolant fan -V7- when refrigerant circuit pressure increases.
High Pressure Sensor -G65-
NOTE: Depending on engine type, refrigerant Systems have either an A/C pressure switch -F129- or high pressure sensor - G65- installed. Refer to appropriate wiring diagram.
Sensor -G65- -B-, transmits a square wave signal to Coolant Fan Control (FC) Module -J293- at a rate which varies according to the refrigerant system pressure. The signal is processed as follows:
Based on the signal transmitted by -G65-,-J293- determines the A/C refrigerant system pressure and controls A/C clutch -N25- and coolant fan functions accordingly. For example:
- Switches the radiator fan -V7- to the next higher speed when pressure in the refrigerant circuit increase.
- Switches off A/C clutch -N25- when pressure is excessive (for example when engine cooling is insufficient).
- Switches off A/C clutch -N25- off when pressure is too low (for example with low/no refrigerant).
The -G65- signal is also input to the Motronic Engine Control Module (ECM). As the amount of torque needed to drive the A/C compressor varies according to refrigerant system pressure, the ECM processes this signal in order to enhance engine performance.
Depending on the type of ECM, this signal may or may not appear as a duty cycle on the read measuring value block display (function 08), -G65- signal, refer Fig. 3 in "A/C Refrigerant System, Servicing" Service and Repair
A/C System Hoses and Lines
The mixture of refrigerant oil (PAG oil) and refrigerant R-134a attacks some metals and alloys (for example, copper) and breaks down certain hose material. Use only hoses and lines that are identified with a green mark (stripe) or the lettering "R-134a".
Hoses and lines are fastened together with threaded couplings/fittings and are retained (to bodywork or components) with specially isolated hose clamps.
NOTE:
- During servicing, all couplings, fittings and related fasteners must be torqued to specifications. Refer to "A/C Refrigerant System, Replacing Components" Service and Repair
- Ensure that only special tools (as specified) are used while servicing.