Auto Repair Q&A



Cooling System










Auto Repair Products

A/C Compressor Problems - Clutch, Compressor, or Something Else?

Auto AC system

This is the time of year when drivers begin to notice that their air conditioning system (A/C or HVAC) isn't working. As the weather warms up, A/C systems are switched on and trouble can start to brew. Recently in our forums, user Alabamacowboy had a problem with his Ram 1500's A/C compressor.

Unlike most who may just have "no cold air," Alabamacowboy at least realized where the trouble was right off. The air conditioning compressor kept clicking on and off, which mechanics call "short cycling." This is a common problem that is usually an issue with the compressor's engagement clutch or the controls for it.

Assuming all we know is that the compressor isn't engaging or staying engaged, let's look at the steps for narrowing the problem down to the clutch.

Diagnosing A/C Clutch Problems

Begin by turning on the engine and then turning the climate controls to air conditioning with the fan on medium or higher. You should be able to readily feel the forced air pushing through the vents. Wait for a few minutes and if the temperature does not lower, begin diagnostics at the A/C compressor.

Opening the hood, observing all cautions for doing so when the engine is operating, look to see if the A/C compressor is engaging. Switch off the A/C in the car and listen to see if the engine "picks up" briefly as the compressor's load is relieved. Have a friend turn the A/C back on and listen for the engine taking on the extra load and for the "click" of the A/C clutch engaging. If after a few tries you cannot get the compressor to engage, you can now rule out leaks or seizing of the compressor as your most serious problem. If you do hear the clutch engage and the compressor's pulley stops turning and the belt squeals over it, you have a seized compressor that requires replacement.

Your next step is to check the A/C compressor clutch coil. We outlined this by linking to an ASE study guide explaining the process. In short form, you're first testing the circuit for continuity and proper resistance and then "jumping" the connection to bypass the relay and force the clutch to engage. The idea is to test whether the clutch or its fuse/relay are bad. You can read the proper steps at this link.

Through those steps, you should have diagnosed the clutch or relay issue and will know what to replace for a fix. This was the issue Alabamacowboy was having and a clutch replacement likely fixed his problem (he did not get back to say one way or the other).

Not the clutch?

If the clutch engages, the compressor works, and the system is still blowing warm or hot air, you have a problem in your HVAC box under the dash or are low on refrigerant. Do a pressure test of the refrigerant system to make sure it's pressurized to spec. If so, you likely have a problem with the servos opening and closing the HVAC vents and are getting air from the heater core or fresh outside the car without it passing over the A/C to cool first.

See this article for more information on diagnosing those non-leak, non-compressor issues.