A/C Refrigerant System, Component Overview
A/C Refrigerant 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 may be identified with a green label.
Receiver drier
The receiver drier acts as a refrigerant reservoir for the system. Any moisture in the system forms as droplets and is absorbed in the drier desiccant.
NOTE: To ensure optimum system operation, replace receiver drier every time refrigerant system is opened.
CAUTION: The receiver drier may be identified with a label that indicates the drier desiccant inside is only compatible with R-134a refrigerant. NEVER use an R-12 receiver drier in and R-134a system.
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 as such with a 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 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 air outlet excessive pressure. When the system pressure is reduced, the valve closes to prevent total refrigerant loss.
An adhesive cap on the end of the pressure relief valve pops out when the valve has opened.
A/C pressure switch -F129-
-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.
NOTE:
- The presence of -F129- is engine dependant. Where -F129- is not used, high pressure sensor -G65- is used instead.
- Always confirm system use of either -F129- or -G65- and applicable wiring circuit using applicable "Engine" and "Air conditioning" wiring diagrams.
High pressure sensor -G65-
Where applicable, high pressure 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. -J293 reacts to the pulse rate of the signal from -G65 as follows:
- If the refrigerant system pressure rises, -J293- switches the radiator fan(s) to the second speed.
- Where excessive or insufficient refrigerant system pressure is present (E.g.: insufficient air flow over condenser or when overcharged), -J293- switches A/C clutch -N25- off (-N25- controlled by -J293-).
- On Climatronic equipped models it informs the A/C control head -E87- that the pressure in the refrigerant system is OK and that A/C clutch -N25- can be switched on (-N25- controlled by -J293-).
On applicable engines, the signal generated by -G65- is also provided as an input to the Motronic Engine Control Module (ECM). As the amount of torque needed to drive the A/C compressor varies according to the refrigerant system pressure, the ECM processes this signal in order to enhance engine performance.
NOTE:
- The presence of -G65- is engine dependant. Where -G65- is not used, A/C pressure switch -F129- is used instead.
- Where -G65- is used, it's wiring circuit varies according to engine application (E.g.: some are connected to the ECM, some are not).
- Always confirm system use of -G65- and applicable wiring circuit using applicable "Engine" and "Air conditioning" wiring diagrams.
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 factory specified replacement hoses and lines.
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.
- Ensure that only special tools (as specified) are used while servicing.