Hi,
I am trying to avoid further diagnostic costs and misguided solutions from my mechanic with regards to my A/C compressor cutting out on me and blowing warm air.

Here is what happens: when the outdoor temperature exceeds 85 degrees, my car's A/C will stop functioning after about 20 minutes of driving time. If the temperature outdoors is not very hot, the A/C runs perfectly cool the entire time, and the compressor does not stop working. I have successfully driven for over an hour in cooler temperatures with the A/C on, no problems with cold air coming out of the vents.

I have recently had the A/C charged and the system was checked for leaks. No leaks, and it is now full of new coolant. Also, I have an 18 month old alternator, the previous was replaced due to failure. I don't believe my alternator is failing, but I cannot be certain until it's tested. On that note--is a weakened alternator likely to cut out the A/C in order to maintain its required amperage? The previously failed alternator did not fail outright, it was pushing 12.8 amps rather than 13.5. Over time (30+ minutes), the car would completely die. It was a difficult diagnostic since the previous mechanic didn't realize the partial failure of the alternator.

My other thought is the compressor is failing. How can I better diagnose this problem in order to avoid further unsuccessful trips to the mechanic in the next couple of weeks?