Compressor HVAC: Description and Operation

The Variable Displacement Compressor (VDC) that matches the automotive air conditioning demand under all conditions without the clutch cycling. The basic compressor mechanism is a variable angle wobble plate with six axially oriented cylinders.

Changing the piston displacement is achieved by changing the wobble plate angle which is accomplished by controlling the crankcase-suction pressure differential. As angle increases, the displacement increases, as the angle decreases, the displacement decreases.

When the heat load at the evaporator decreases, (or when rpm increases) the suction pressure decreases. The suction pressure is sensed at the main control valve which then directs high discharge pressure into the crankcase. The result is a small wobble plate angle and therefore, a small piston displacement, which is needed when the heat load is small.

When the heat load at the evaporator increases, (or the rpm decreases) the suction pressure increases which causes the main control valve to close off discharge pressure to the crankcase. As the crankcase pressure reduces, the wobble plate angle increases, therefore increasing the piston displacement, which is needed when the heat load is high.

When quick cooling is needed the sub-control valve allows for quicker release of crankcase pressure to the suction side.