Externally Controlled Variable Displacement Compressor

WARNING: This page is about a different car, the 2014 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Variable displacement compressors operate at lower pressures (compared to fixed compressors) and depend on correct system charge for normal operation.

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:

A 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.
Uses Motorcraft® Polyalkylene Glycol (PAG) Refrigerant Compressor Oil YN-12-D. 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.

Refer to the oil adding procedure specified for this vehicle when installing a new A/C compressor. Refer to Refrigerant Oil Adding .

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, resulting in the target evaporator core temperature. The target evaporator core temperature range for the DATC system is 3-8°C (37.4-46.4°F); 3-5°C (37.4-41°F) for the EMTC system.

The PCM pulse width modulates the ground to the externally controlled variable displacement compressor control valve to change the A/C compressor displacement by changing the swash plate angle based on the following items:

Ambient air temperature
Engine revolutions per minute (RPM)
Evaporator temperature
High side and low side A/C pressures
Temperature and mode settings of the climate control head