ac trouble

I am having troubles with my air conditioner in my 1999 GMC truck. The compresser doesn't kick on. However, when the relay under the hood is removed, I can jump it across wire and AC kicks on and works great. I've tried various relays that I know work, but the wire seems to be the only thing that kicks the compresser on. Freon levels also okay. Any ideas?

How did you determine that you have enough R-134 in the system? Is it showing 250-300 psi on the high pressure side? Are you are only going by what you see in the receiver/drier sight glass? If you are mistaken, and have bypassed the low pressure cut-out you'll damage the compressor.

You are low on refrigerant. By bypassing the relay you are overriding the low pressure switch.

You need to get it recharged and diagnosed for a leak.

Hope this helps.

You are low on refrigerant. By bypassing the relay you are overriding the low pressure switch.

You need to get it recharged and diagnosed for a leak.

Hope this helps.


GM is known for there low pressure switches being bad they only cost $15.00 and one minute to change. But make sure your pressure are good first. I have changed 20 or more in the last 2 years and I only do this on the side. Good luck