Compressor HVAC: Description and Operation

DISCRIPTION
The Variable Displacement Compressor (VDC) provides maximum air-conditioning performance in most ambient conditions. It is designed to operate continuously without any cycling of the compressor clutch. The basic compressor mechanism is a variable angle wobble plate with six axially oriented cylinders.

OPPERATION
The compressor will change displacement to match the vehicle air conditioning demand. The pumping stroke is governed by the pressure differential of the suction and the crankcase pressures. When the suction pressure is higher than the crankcase pressure, the wobble plate angle in the compressor will increase. When the suction pressure is lower than the crankcase pressure, the wobble plate angle will decrease and so will the compressor pumping stroke. When the heat load at the evaporator decreases or when compressor RPM increases, the suction pressure decreases. This causes the main control valve to open and allow high pressure discharge gas to bleed into the crankcase to increase the crankcase pressure. The elevated crankcase pressure will reduce the wobble plate angle or reduce the pumping stroke. When quick cooling is needed at the system starting up, the sub-control valve is opened for quicker release of crankcase pressure to the suction side. Under high heat load conditions, the main control is completely closed.