Why does the AC compressor shut down in very hot weather but work ok in the AM?

Bottom line the compressor was not engaging.

First thing we tried, replaced the low and the high pressure sensors. (About $20 each)

It was an easy fix but that didn't work.

Second thing we tried, was the AC relay and swapped it out with another "known good" one.

This is another easy fix to see if you have a bad relay but that didn't work.

Third thing we tried, measured the voltage to the compressor.

Voltage to the compressor was 12V. Hmm... now we are getting somewhere.

Fourth thing we tried, was looked up the specs on the compressor and found that the coil should be around 4-5 ohms. In the hot state it would go upto 24 ohms. So as best we could figure, the heat cause the coil to expand and caused the circuit to open.

In a compressor when your AC turns on the coil is charged and it pulls in the clutch which is attached to you belt. Once the clutch is pulled in the compressor will turn.

Back to the solution... you can buy a new clutch without breaking the system and having to mess with the freon. After talking to a few mechanics I decided to to just buy a new compressor in a kit that comes with everything you need. Replacing the compressor is not really all that hard if you have a gauge set and a vacuum pump. With everything I had to buy it was about $400 but I already had the vacuum pump and gauge set.

... but I still saved because most dealerships want $800 - $1200 to do the same thing.

One thing they can do is flush the system out to remove any contamination in the system. O'well at least I have cold AC again and I didn't have to pay for labor. Hope this helps ya'll.