Compressor HVAC: Description and Operation

General
The variable compressor is basically a swash plate type that changes piston stroke in response to the required cooling capacity.
The tilt of the swash plate allows the piston's stroke to change so that refrigerant discharge can be continuously changed from 14.5 to 184 cubic.cm (0.885 to 11.228 cu in).

Operation
1. Operation Control Valve
Operation control valve is located in the suction port (low-pressure) side, and opens or closes in response to changes in refrigerant suction pressure.
Operation of the valve controls the internal pressure of the crankcase.
The angle of the swash plate is controlled between the crankcase's internal pressure and the piston cylinder pressure.




2. Maximum Cooling
Refrigerant pressure on the low-pressure side increases with an increase in heat loads.
When this occurs, the control valve's bellows compress to open the low-pressure side valve and close the high-pressure side valve.
This causes the following pressure changes:
^ the crankcase's internal pressure to equal the pressure on the low-pressure side;
^ the cylinder's internal pressure to be greater than the crankcase's internal pressure. Under this condition, the swash plate is set to the maximum stroke position.




3. Capacity Control
^ Refrigerant pressure on suction side is low during high speed driving or when ambient or interior temperature is low.
^ The bellows expands when refrigerant pressure on the suction pressure side drops below approximately 177 kPa (1.8 kg/Sq.cm, 26 psi).
Since suction pressure is low, it makes the suction port close and the discharge port open. Thus, crankcase pressure becomes high as high pressure enters the crankcase.
^ The force acts around the journal pin near the swash plate, and is generated by the pressure difference before and behind the piston.
The drive lug and journal pin are located where the piston generates the highest pressure. Piston pressure is between suction pressure Ps and discharge pressure Pd, which is near suction pressure Ps. If crankcase pressure Pd rises due to capacity control, the force around the journal pin makes the swash plate angle decrease and also the piston stroke decrease. In other words, crankcase pressure increase triggers pressure difference between the piston and the crankcase. The pressure difference changes the angle of the swash plate.