Externally Controlled Variable Displacement Compressor
Variable displacement compressor internals are similar to fixed displacement compressors. The pistons are placed around an angled plate (swash plate) and are pushed back and forth as the plate rotates. Variable displacement compressors vary the swash plate angle to allow piston displacement to vary from 5% (default) to 100% of full capacity to meet cooling demand.
The externally controlled variable displacement compressor has the following characteristics:
- non-serviceable shaft seal.
- a non-serviceable pressure relief valve installed in the rear of the compressor to protect the refrigerant system against excessively high refrigerant pressures.
- For the appropriate refrigerant and refrigerant oil, Refer to: Specifications .
- This oil contains special additives required for the A/C compressor. The oil may have some slightly dark-colored streaks while maintaining normal oil viscosity. This is normal for this A/C compressor because of break-in wear that can discolor the oil.
The piston displacement of the externally controlled variable displacement compressor is controlled by a PWM signal from the PCM which electronically drives the control valve. The control valve drives the crankcase pressure and thus the swash plate angle. The externally controlled variable displacement compressor achieves precise cooling capability based on the cabin temperature and driving conditions.
The PCM pulse width modulates the ground to the externally controlled variable displacement compressor control valve to change the displacement of the A/C compressor by changing the swash plate angle based on the following items:
- Ambient air temperature
- Engine RPM
- Evaporator temperature
- High side and low side A/C pressures
- Temperature and mode settings of the climate control head