Thanks in advance for the help and I apologize in advance for the long post.
11 months and 3 weeks ago a mechanic I trust replaced my a/c. Two weeks later I rear-ended another car.
There was minor cosmetic damage but it ran as before. A week after that began the record setting Texas summer heat wave and my car got so hot the mirror gauge registered 125 in a fast food line. This is the only time it got that hot. Once we got moving everything seemed fine.
A couple of days later the a/c ran for about 10 minutes then stopped. Slowly the time the unit cooled decreased until it stopped working. I took the car back to the mechanic. He stated the pressure measured up to 100 psi and the temperature was above the rating for the a/c system.
He fixed a short in the radiator/engine fan, the temperature problem never returned and the pressures were high but my a/c worked.
At first the a/c seemed to work fine but then it began to work only sometimes. When it did work it would sometimes work in “hybrid” mode which you Saturn owners recognize as cooling at the reduced level that saves gas in stop and go traffic – or not at all as we say in TX.
I took it back. The mechanic now explained the I’d voided the warranty because the short in the radiator fan allowed the car and a/c system to get too hot. The high heat had burned some sort of internal valve in the compressor.
The valve is unreliable. The performance of the a/c is mainly temperature dependent. The hotter the day the less likely the a/c will produce enough of a pressure difference to open this valve. Warm days the system will probably cool. Hot days it will probably not.
Being a CarTalk listener and an former nerd I thought of and tried a way to magnify the pressure difference using rpm. It works but the hotter the day the higher and longer I have to rev the engine.
Now I’m burning oil for the fist time ever.
Did I cripple my air conditioner or does my trusted mechanic learn a little to little when he learned to repair my hybrid a/c system?
I think you need a 2nd opinion. I don’t know where he pulled 100 PSI from. That could be high for the low side, but would be ridiculously low for the high side. The A/C system has built in controls to shut it down if the temps or pressures are unacceptably high or low.
You say you’re burning oil for the first time… did the car ever overheat when the radiator fan wasn’t working?
The one year warranty expires in two day. I’m taking it back in and hear what they have to say one more time. I’ll look up the shop manual pressure ranges before I go in.
What can you tell me about the mystery mystery valve in the system that has to have the high rmp to kick in?
It got hot just the one time but I took it back to the shop right away.
I’m thinking I’m burning oil because of the high rpms needed to get the a/c to kick in. I’m revving the engine up to 4k until I get cold air. It doesn’t take that long for the system to kick in.
If the radiator/condenser fan failed the engine would over heat when stopped or driving slowly and the AC high side pressure would rise significantly. A long period of idling could damage the engine and the AC. The AC compressor has a high pressure safety release (blow off) valve and a super heat switch to protect from high heat/pressure but often those devices allow the pressure to exceed 375 pounds and although nothing explodes, internal damage is done. I don’t believe that automotive AC systems will ever be built to withstand 125* ambient temperatures and even if the radiator fan had been operating the AC would need to be turned off to allow the engine to get the full benefit of the fan.
Adding an additional fan, or even 2 fans, at the front of the radiator/condenser is sometimes needed to enable driving at low speeds or extended idling in high temperature. An especially hot summer some years ago set records with 100+ degrees for weeks and a fleet of shuttle buses were impossible to keep cool until the extra fans were added.