AC Question

I have a 99 Malibu. It's been a jewel since I bought it new. At the beginning of the summer, the A/C wasn't cooling so I added about 1 1/2 cans of R134a. I got one of the refill kits that comes with a pressure gauge for the low pressure port.

Anyway, I filled it to the correct pressure based on the outside ambient temperature. The AC worked well all summer. For about three weeks, I've been driving my truck and the car hasn't been driven. Today I drove the Malibu to work. This morning the temperature was about 76 degrees F. The AC was super cold...had to run it on its lowest level. This afternoon, after work, I went out to get in the car to come home. The outside temp was about 95 degrees at this point. When I cranked up the car, the AC came on and blew cool air for about 30 seconds and then stopped. Nothing I could do would get the AC to blow cold. I checked under the hood and sure enough the clutch wasn't engaging on the compressor.

I assumed that this probably meant the freon was low again so I got home and tried to add another can of freon. It wouldn't even go in and the gauge said that the pressure level on the low side was maxed out.

So, I have a couple of questions. 1 - if the pressure were too high, would it keep the compressor from coming on? 2 - at the beginning of the summer, the days weren't quite so hot...could the rise in temperature cause a rise in the pressure? If not, would could account for that?

I can't figure out why it worked so well this morning when things were cooler, but this afternoon...nothing.

Btw, here's what I've tried:

1 - took control head off and cleaned it just to make sure (had problems with that in the past)
2 - checked all fuses and relays for the compressor and AC
3 - tried "venting" a little of the freon from the low pressure side to bring the pressure down (I know that's not environmentally correct, but just a little to try my hunch)

Anyway, none of this worked. Admittedly, it's still in the red as far as pressure goes on the gauge so I don't know if I vented enough to really make a difference if the pressure would have any affect on things.

Any advice would be greatly appreciated. I love this car, but don't have a lot of money to sink into the AC system of a 14 year old vehicle.

Thanks!!!

18 oz, most likely over filled. The proper way is to evacuate and add factory amount with dye, for leaking checking.

you need to buy a manifold gauge set. That will give you the best starting point to work from. If you have pressures, and the pump is not kicking in, Could be several things.

1)head unit
2) compressor (clutch etc)
3) ecu

My head unit went completely bad (98 olds cutlass same as malibu), bought one from junkyard for 20 bux, cleaned contacts with deoxit gold, and it run like a champ.

Coompressor has to be running for the gage to mean anything-otherwise you are reading static pressure....

Have you scanned for codes? I think this system uses a 3 wire pressure sensor....if it set a code in the PCM, the PCM will inhibit operation of compressor...