intermittant ac

[oldmxer]

in the dark AM going to work it seems to be ok. here in TX its getting over 100 on way home. if I manage to get on the highway it does ok but if I get stuck in traffic or stop for a fw minutes the compressor stops cycling on. it may or maynot resume when I get moving again, sometimes this results in no more cooling until next morning. I have worked on all my cars ac for many years but this one has me beat. I put my gage on while its working and freon is good and when it is working it blows cold as ever. it seems to be ambient temperature related. I suspect it is high/low four wire pressure switch. but I bypassed it according to schematic and thought I had it but still finds reason to quit. cant come up with why it seems to be ambient temp related.

[Sponsor]

[cbdallas]

A friend's Corvette did this a lot. A/C worked great in the morning, but in hot afternoons it would blow cold for about 2 minutes, and then the compressor would slow, & eventually stop cycling. Turned out to be a faulty pressure switch. It's a safeguard to prevent the compressor clutch from locking if it detects low freon pressure. It had plenty of freon, but the switch had a different opinion.

[oldmxer]

thanks for the info, that kind of reinforces my gut feeling that it was one or both pressure switches. I will more than likely just replace both switches and recharge it and see if that fixes it since that will be a heck of a lot cheaper than takin it to the dealer. I will post the results in case it will help someone else.

[whynotthinkwhynot]

The pressure switch should have a ball valve to prevent refrigerant from leaking, so no recharge needed.

Good luck with that but the problem might be something like the diode.

How cold is your air in the morning? Is it just barely cold, or is it very cold?

[oldmxer]

when it is working the air is very cold as it was when new, regardless of outside temp. If the pressure switches can be changed without loss of freon because of a ball valve how does the ball valve allow the pressure to get to the switch?

[whynotthinkwhynot]

Because the switch pushes it in when you screw it in all the way.

[oldmxer]

I realized that as soon as I hit post, I blame it on my heat muddled brain!
I replaced main pressure/cycling switch when I got home and it hasnt missed a beat yet, big test will be if it stays on today in the afternoon heat.

[oldmxer]

EUREKA!, replacement of 2 wire pressure/cycling switch did the trick. I suspect the switch may not have been bad tho because when I put the wrench on it it was loose, this may explain why it worked when cold but not when hot, the post that pushes on the valve to let freon get to switch was probably barely letting gas get past and when it heated up it was just enough to restrict flow. lesson learned