A/C Refrigerant System, Component Overview
A/C Refrigerant System, Component Overview
Compressor with A/C Clutch
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.
Refrigerant system pressures and A/C outlet temperatures are regulated by cycling the A/C clutch on and off according to the selected temperature.
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.
Compressor without A/C Clutch
The compressor is driven continuously via a belt on the engine.
Low-pressure refrigerant gas from the evaporator is compressed by the compressor. After compression, the refrigerant gas (now high-pressure) flows to the condenser.
Refrigerant system pressures and A/C outlet temperatures are regulated by external control of A/C Compressor Regulator Valve N280.
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 system is equipped with a sight glass, a properly charged A/C system can be confirmed when, with the A/C Clutch engaged and engine running at 1,500 RPM, the sight glass remains clear and bubble free.
NOTE: The mixture of R-134a refrigerant and refrigerant (PAG) oil may appear milky in the sight glass.
Expansion valve
The expansion valve restricts and controls refrigerant flow to the evaporator. This lowers the refrigerant temperature, pressure and initiates refrigerant change of state from fluid to vapor prior to the evaporator.
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.
A/C Pressure 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 condenser 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.
High Pressure Sensor G65 - B -, transmits a square wave signal to Coolant Fan Control (FC) Control 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 High Pressure Sensor G65, Coolant Fan Control (FC) Control Module J293 determines the A/C refrigerant system pressure and controls A/C Clutch N25 and Coolant Fan functions accordingly. For example:
- Switches the Coolant 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 High Pressure Sensor 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.
High Pressure Sensor G65 signal, checking.
A/C Compressor Regulator Valve N280
On A/C compressors without A/C Clutch N25, the A/C Compressor Regulator Valve N280 is integrated with the A/C compressor. Its function is controlled by the Motronic Engine Control Module (ECM) J220 in accordance with engine loads, speed and engine coolant temperature. The valve regulates the low pressure (suction) side of the A/C compressor, thus controlling the evaporator temperature.
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.
- Ensure that only special tools (as specified) are used while servicing.