I installed a brand new compressor. It worked fine for about a week, then warm air came in through the ducts. There was a vacuum leak and an o ring that was bad, and fixed that. It was fine for a day, then warm air again.I checked the fuse inside the car that operates the a/c and that is good. I haven't checked the relay fuse in the engine compartment. I don't know how to check for a bad relay . Does it look like a regular fuse?I know the fuses inside the car have the wires you can check. Are relay fuses expensive?Thanks to all for your responses.

 

Forgot to mention, if it matters. I have a 1999 F150 4.2 5 speed.

 

You most likely have a leak. Nowhere did you mention that you took any pressure readings.

Did you perform a vacuum leak-down test to verify the integrity of the sealed system?

Steve

 

There is a leak.
An AC shop can diagnois it and repair it for less than a consumer can fiddle with it till the actual bad part get fixed.

 

I guess my mistake was having my wifes Nephew fix it. Acually, he is a Mercedes mechanic and farmed the job out. He said they did found a leak and pressure tested it and everything worked fine for about a week. So , you think it';s still a leak? I thought possibly it could be the clutch relay, but that's why i'm here, to find out. UCLA all the way!

 

If there isn't enough refrigerant in the system, the compressor will never come on. A '99 has ultraviolet dye in it from the factory - start looking for leaks with a blacklight.

 

Put a damned pressure guage on it and check.

We can't do that from here.

If it has leaked and the pressure is too low, you can replace every relay etc in the system and it still won't work.

Steve