The air-conditioning compressor circulates refrigerant through the air-conditioning system. It is normally driven by a belt from the engine crankshaft.
Four basic types are used. Reciprocating Piston, Rotary Vane, Scroll and Axial Piston.
The Axial Piston type is one of the most common.
The cylinders are placed around the drive shaft and parallel to its axis. Each cylinder has a doubled ended piston, allowing a separate pumping chamber at each end of the cylinder.
Each pumping chamber has a set of inlet and discharge valves. The inlet reed valves are connected to the inlet port of the compressor by drillings. The discharge valves are connected to the discharge port - also by drillings.
A swash plate is attached to the drive plate at an angle. Rotation of the drive shaft causes the outer edge of the swash plate to constantly change its linear position.
The pistons are connected to the outer edge of the swash plate by swiveling ball joints. The action of the plate and ball joints continually moves the pistons back and forth in the cylinder.
As the volume above a piston increases, the refrigerant is drawn into the cylinder through the inlet reed valves. When the volume above a piston reduces, the refrigerant is forced out of the cylinder through the discharge reed valves.
As one end of the cylinder is on the intake stroke, the other end is on the discharge stroke. This dual pumping action occurs in each cylinder during each revolution of the crankshaft.