When the AC works it blows nice cold air, problem is that it won't work for more than a few minutes.

Basically, I have to turn the AC off for about 5 minutes before turning it on again. Then it will work for a couple minutes before it warms up. If I repeat this process enough (like on a long drive) it will eventually stay cold.

I'm not even sure where to start looking. Any ideas?

 

sounds like it just needs charged, i would start by checking the pressure

 

Well, I bought a manifold gauge and measured about 50 psi hi/ 25 psi low while the compressor was running. I thought that seemed low but I didn't have a can of r142a.

The next day I got a can and was ready to add some more refrigerant.... I don't know what I messed with, but now the compressor will not turn on and both hi/low side pressures are reading about 150psi.

Could I have messed something up just by checking the pressure?

 

150 psi not running is pretty normal.

50/25 is WAY low.

Dump in a can of cold juice.

Should run; most likely, you bumped a wire loose somewhere, or some such.

 

Don't add any refrigerant.

It sounds like your "low pressure cycle switch" needs replacing. After running for awhile and your A/C gets down to cold temp, instead of cycling the compressor off for a couple of seconds, the compressor will just stop and not come back on. The duct temps will get warmer since all the cold from the evaporator will warm up and start blowing warm air into the car.

50/25 psi......I'm assuming you mean 50/250 psi with the system running. If so, you have PLENTY of refrigerant in there. Adding more would give worse performance.

The deal with refrigerant is that it's a medium to transfer heat with. So in that regard, more refrigerant allows you to transfer more heat (to the atmosphere....the left over air is thus cold and blows on you). Too little refrigerant has less capacity to transfer heat and it's very easy to compress. Hence why compressors cycle rapidly when they're low on refrigerant.

Consequently, having too much refrigerant is also bad. Because while it has extra capacity to transfer heat. It's also harder to compress. Thus you run higher pressures and get less cooling performance. If the system is overcharged and/or has air inside the system (which is VERY hard to compress), you will trigger the high pressure cut out switch (the plug on top of the compressor)

Ultimately it's a balancing act in terms of the best quantity of refrigerant. In Phoenix in August a car would do better with slightly less refrigerant (to keep the pressures from being too high). In San Diego in May, a car would do better with slightly more refrigerant (to keep the pressures from being too low.)

Getting back to my 1st paragraph. A low pressure cycle switch should be available at most parts stores. They look like this: https://www.ackits.com/pc/29-30401/P...essure+Cut-Off

You can safely unscrew the factory one. It will let out maybe a millisecond of refrigerant. But it closes the hole when you unscrew the factory one. (Basically the same as when you check your tire pressure. You get a tiny spurt of air come out and then nothing comes out)

 

He said

Don't

ANYTHING.

Apart from that, good advice; too much refrig is just as bad as not enough. However,

pretty much seals the deal.

Not enough.

Add more.

 

I'm having a heck of a time adding more refrigerant.

Last night it was still pretty warm outside. The compressor would not kick on and the low side pressure was readying over 100psi. This morning the low side pressure was about 30psi and the compressor kicked on. I thought I was ready to go, but the compressor turned off and wouldn't come back on. None of the refrigerant entered the system...

Any idea what could be going on?

 

I've been looking into this issue a bit and read that the radiator cooling fan is supposed to come on when the AC is turned on, is that correct? My cooling fan only comes on when the engine is really hot (e.g. idle on a hot day).

I have a 92 3.1L V6 with a single radiator cooling fan.

 

There is a pressure switch in the hard line that runs between the condenser and the evaporator, depending on the year some are normally open or normally closed. Depending on which one you have the switch will open or close when the pressure reaches a certain level. That signal is sent to the ECM which will then turn on the fan. If your charge is low the pressure will not reach the level needed to activate the switch or may only trigger the fan for short periods.

 

I was stuck in traffic for an hour a few days ago when it was 90°F outside and my AC worked perfectly the whole time. Then on my way home it wasn't working at all... It was driving me crazy.

I finally started poking around some more. I jumpered the low pressure switch and the compressor and fan kicked on for about a minute, then the compressor and fan both stopped working...

I eventually tapped on the compressor relay and it kicked on! It turned off after a few seconds, I tapped the relay again and the compressor came back on. I did this a few times. Looks like it might just be a bad relay.