Compressor (B8444S Only)
The compressor is mounted directly on the engine block and is driven by the engine crankshaft via the auxiliaries belt.
In the refrigerant circuit, the compressor is located between the evaporator and the condenser.
The compressor has variable displacement that is regulated by a replaceable solenoid, which is located on the underside of the compressor. The temperature sensor situated after the evaporator sends a signal to the Climate Control Module (CCM), which uses the signal to control the solenoid.
Compressors with variable displacement usually do not switch off during normal operation. The flow of refrigerant is continually adapted based on need. The compressor works between min. and max. displacement due to the following:
- the pistons are driven by a cam disc with a variable angle
- the angle is determined by springs if the compressor is disengaged
- if the compressor is engaged, the angle is determined by the pressure exerted on the top of the pistons (= intake pressure) and the bottom of the pistons (= pressure in the crankcase) during the intake phase
- the pressure on the bottom of the pistons (= in the crankcase) is regulated by a solenoid that is controlled by the Climate Control Module (CCM).
If intake pressure is high, the compressor works to increase displacement.
- The solenoid opens and lowers the pressure in the crankcase. The counterpressure on the back of the pistons then reduces and the cam disc angle increases.
- The increased angle generates increased stroke, which causes a greater amount of refrigerant to be "sucked in" and a drop in intake pressure.
When intake pressure is low, the compressor works to reduce displacement.
- The valve closes and pressure in the crankcase increases. The pressure is built up by refrigerant that is led from the outlet side to the crankcase via a calibrated duct. The counterpressure on the back of the pistons then increases and the cam disc angle decreases.
- The decreased angle generated reduced stroke, which causes a smaller amount of refrigerant to be "sucked in" and an increase in intake pressure.
The compressor is also regulated by the A/C pressure sensor, which deactivates the system if pressure becomes too high.
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 is the component of the climate control system with the largest mass. Thus, it takes the longest to warm up. In climates where the temperature varies greatly from night to day, it is often the compressor that is the system's coldest point each morning. Thus, all the refrigerant in the system makes its way to the compressor crankcase. Upon start, it takes 1-2 minutes for the refrigerant to evaporate. During this period, it may seem like the climate control system is not working.