Variable Displacement Compressor
A variable displacement compressor eliminates the need for a cycling clutch by altering the compressor’s volume based on system demands. A variable displacement clutch system's clutch is left engaged while the system is in use. They are disengaged only if there’s a problem or when not in use. There is no cycle switch to cycle the compressor on and off. The displacement or output of the compressor is altered by changing the stroke of the pistons.
The pistons are attached to an axial wobble plate that changes angle based on the difference in pressure between the top of the piston and the housing. When cabin temperatures are warm and air conditioning demand is high, the low side pressure will also be high. During this time, the compressor’s wobble plate is moved to its greatest angle, increasing the piston's stroke and providing maximum refrigerant displacement. As demand decreases, the wobble plate is moved to a lesser angle providing lesser, or minimum output.
This is accomplished with a control valve connected to the suction and discharge ports in the compressors head. This valve may be a mechanically or a computer controlled valve. The mechanical valve has a diaphragm that responds to changes in low side pressure. As this valve opens, it increases piston stroke. As piston stroke increases, so does the volume or displacement of the refrigerant’s flow through the compressor.