A/C Pro

#PoptheHood: A Dipstick’s Guide to Compressors


What is a compressor and how does it work?

The compressor is often considered the “heart” of a vehicle’s air conditioning system. It’s the most vital component in the system. The compressor pulls the refrigerant out of the evaporator and pushes it into a condenser, and then back into the evaporator to complete the cycle. A compressor is an electro-mechanical pump, driven by a belt that’s attached to the engine’s crankshaft; however some newer versions can be driven by electricity with no belt. This pump moves the refrigerant through the continuous loop that is the air conditioning system. The refrigerant is carried by rubber hoses and aluminum pipes from one component to another. There are various types of compressors (piston, wobble plate, scroll, etc.) used in automotive air conditioning systems, but they all work to accomplish the same objective – transforming refrigerant from a low pressure vapor to a high pressure, high temperature vapor and circulating it through the A/C system.

Compressors can fail for many different reasons: bad fuses, wear and tear, age, a wiring problem, improper maintenance, a broken AC switch in your dash, etc. Keep in mind, A/C compressors are designed to only come on when there is enough refrigerant to compress. So, if your compressor is not running, that could be a sign that it is working as designed, and simply needs more refrigerant. Most systems have a low-pressure safety cutout that will disable the compressor if there isn’t enough refrigerant in the system. The first thing you’ll want to check is if your compressor is engaged.

How can I tell if a compressor is engaged?

If the compressor is engaged, the center of the compressor clutch will turn with the outer pulley, on certain types of compressors.  (Please note that on variable displacement compressors the center of the pulley can be spinning at all times.) Check out our video showing a properly running compressor.   If you have specific questions about whether your compressor is working properly, please consult a professional certified A/C mechanic.

How do I recharge my A/C system?

If you determine your compressor is functioning properly, you can check your refrigerant using an A/C Pro gauge to determine if low refrigerant levels are at the root of warm air blowing from your system.  The following video with guide you through the steps needed to check refrigerant levels and recharge you’re A/C system.

If you do run into any questions about how to use A/C Pro or would like additional help, you can always contact the pros online or by phone.