Compressor (not B8444S)
The compressor is located at the front of the engine. The air conditioning compressor is installed on the auxiliaries bracket which is in turn installed on the cylinder block. There are no bushings between the air conditioning compressor, the auxiliaries bracket and the cylinder block. Direct mounting gives increased rigidity to the mounting. It minimizes the risk of noise.
The compressor is in the refrigerant circuit, located between the evaporator and the condenser.
The compressor has a fixed cylinder displacement.
Compressors with fixed displacement have two limits:
- off
- on.
The air conditioning (A/C) compressor is controlled by an air conditioning (A/C) pressure sensor. The air conditioning (A/C) pressure sensor is positioned on the receiver drier. In vehicles with electronic climate control (ECC), the compressor is also controlled by the temperature after the evaporator.
The compressor is lubricated with specially developed refrigerant oil. This oil (synthetic PAG oil) is mixed with the refrigerant when the air conditioning system is in operation.
The compressor also has a relief valve, located on the rear section of the compressor. The relief valve functions as an additional safety device. The valve opens and releases refrigerant when the pressure in the system is too high (at approx. 3.5 MPa (35 bar)). The valve then shuts again when the pressure has returned to normal.
The compressor is mechanical and is driven by the vehicle engine. When the compressor is operating it "steals" 0.5-8 kW (0.7-11 bhp) from the engine. This may be noticed as slight jerks when driving as the compressor is engaged / disengaged.
The compressor is disengaged for 10 - 20 seconds under full acceleration.
The compressor is the component in the climate control system with the greatest mass. This means that the compressor takes the longest time to warm up. In climates with large differences in day and night temperatures this means that the compressor is often the coldest part of the system. All the refrigerant in the system therefore gathers in the compressor. The compressor cannot compress liquid which means that the pressure becomes very high and there is a risk that the safety valve will be activated when the system is switched on. The safety valve closes when the pressure falls but there is a slight release of refrigerant each time. When the liquid release occurs it also causes a loud noise and shaking.
To minimize the risk of liquid compression the compressor is engaged at the same time as the starter motor is operating. The starter motor has a lower engine speed (RPM) than the vehicle drive motor and the pressure build up in the compressor is not as high. The risk of the safety valve being deployed is minimized and any liquid refrigerant is driven from the compressor.