Types of Auto Compressors

by Jacquelyn Jeanty
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Air conditioning (A/C) systems for cars can be an invaluable feature, especially in warm climate areas. Sitting at the heart of these systems is a device about the size of a large coffee can, called a compressor. The different types of auto compressors vary in how they handle air exchanges between the car interior and the A/C system.


Auto compressors are typically used to power a car's air conditioning system, according to Family Car Parts. A compressor is a pumping device that's fastened to the car engine by a belt assembly. Its main job is to compress and transfer refrigerant gas through the car's A/C system. Because there is more than one way to compress gas, different types of compressors can be used within an A/C system. The most commonly used types of compressors include rotary piston, scroll and variable displacement.


An auto compressor is made up of two sections---a high-pressure area and a low-pressure area. The high-pressure area has a suction that draws the refrigerant gas from the inside of the car and compresses it. Once compressed into a liquid form, it's sent to a condenser area where it works to convert the heat from the inside of the car into cool air. This cool air is then blown into the inside of the car through the low-pressure, output side of the compressor.

Rotary Compressors

Rotary compressors are designed to compress and transfer refrigerant gas using a roller/cylinder mechanism, according to Four Seasons Controlled Climates. The roller rotates inside a cylinder compartment that's divided in two by a spring-mounted blade. This is how the refrigerant is compressed. In effect, the blade creates two sealed off areas within the cylinder. As the roller rotates inside the cylinder, variable pressures build up on both sides of the blade. As pressure build ups on one side, the compressed, cooled gas is forced out on the other.

Scroll Compressors

A scroll compressor is made up of two spiral disks of different heights, with the shorter disk sitting inside the taller one. The tall disk remains stationary while the short disk compresses the refrigerant gas by rotating inside the tall disk. As the short disk rotates, it creates sealed off areas inside the tall disk, which contain varying degrees of pressure. As refrigerant is suctioned into the scroll, some of it gets trapped inside the sealed off areas. The rotation of the short disk causes the gases to move towards the center of the scroll, which is how the gases are compressed. Compressed cooled air then exits the scroll through an outlet along the tall disk wall.

Variable Displacement Compressors

A variable displacement compressor, also known as a reciprocating compressor, is designed to compress and transfer refrigerant gas using a piston/cylinder mechanism. The upward/downward motion of the piston creates varying degrees of pressure that work to suction refrigerant gas into the cylinder, compress it and expel the resulting cool air out into the car's interior. These pressure variations also work to open and close the intake valve, as well as open and close the exhaust valve.

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