Air Conditioner Blowing Warm Air

How to troubleshoot your car's A/C

Published July 29, 2023
Car air conditioner switch

If your vehicle's air conditioner is only blowing warm air, there could be a number of reasons why. You'll need to trace the problem upstream until you find the source. If you're getting airflow, just not cold air, then at least you know the blower motor is working.

Was the onset of the problem gradual?

If the problem arose gradually and worsened with time, the issue could be a dirty cabin air filter that needs to be replaced or a slow refrigerant leak that needs to be fixed. Your A/C operates in a closed system, so a loss of refrigerant is not expected unless there is a leak.

Or did the problem occur suddenly?

However, if the problem appeared suddenly, there's probably another explanation. One easy thing you can check is the vehicle's compressor clutch.

Compressor clutch

The compressor clutch enables the A/C compressor to operate when the engine is running. The crankshaft pulley is connected to several other pulleys including the compressor clutch pulley by means of a drive belt (a.k.a. serpentine belt). Make sure that the belt is not slipping. Refer to a repair guide or YouTube video to identify the location of the compressor clutch pulley. The pulley should always be turning when the engine is running.

When you turn on the A/C, the compressor clutch engages with the pulley, causing the compressor input shaft to turn. When the A/C is off, the pulley turns but the clutch is not engaged. So if you turn the A/C switch and the clutch doesn't engage, you're one step closer to finding the culprit.

Check the relay

One reason the compressor clutch might not be engaging is that the relay that controls it has gone bad. Open up the fuse box and refer to the diagram on the underside of the cover to locate the correct relay. You can test the relay to see if it's gone bad. If you have a matching relay (be sure that they're the same amperage and voltage!), you can swap them to see if that fixes the problem. For instance, on my Corolla, the compressor clutch relay and horn relays are the same, so I was able to swap them to verify that one of them had gone bad.

If the problem is indeed a bad relay, you can purchase a replacement from the dealer or online. You might opt for an OEM one depending on your budget. Once replaced, hopefully that fixes your issue and keeps you running cool again!