Auto Air Conditioning & Heater Repair: on & off AC, gm trucks, pressure switches

Question
I have taken my Tahoe to the dealer ship twice for the same AC
issue.. AC works fine hot or real hot day..
Then starts blowing warm air.. a little latter I turn the system on
again and it works and then blows warm air.. I am tired of
spending money and not finding a solution.. Seems the dearship
wants the money but does not deliver the fix.. They tell me
nothing is wrong with my system and it works fine.
?  

Answer
Hello Carl, Not knowing the year and type of a/c you have,I`am going to try my best diagnosis. GM trucks have a low pressure switch that is located either on or near the accumulator. If you can locate the switch,try to by-pass or jump pass the switch from the harness. You may have a defective switch. The system does not have a thermostatic
control.Everything is controlled by pressure switches. That`s the most common problem is see with GM`s.

Good luck, Davidt