Ford F250 A/C

I have a '99 F-250 with intermittent air conditioning. When the weather is very hot, 85+, the A/C will work fine for 15 to 30 minutes then stop cooling. After 5 to 15 minutes it will start cooling again.

I’ve had the Ford dealer look at it but they couldn’t get it to fail. Another shop had previously looked at it and added R134. This didn’t fix the problem.

When temps are below 80, it seems to work fine.

When it wasn’t cooling, but the contraols were on, I looked underneath and the compressor clutch didn’t seem to be engaged.

Any ideas as to the problem?

Two things that can cause this problem is either the compressor is getting too hot tripping the thermal limit switch on the compressor, or the thermal limit switch on the compressor is faulty.