During hot weather when I turn the AC on after 5 min. of cold air it starts blowing hot air. I have checked the coolant and it's up to pressure. I am able to work on trucks. It's a 2000 Chevy Silverado 1500 LT.
Tough to give you any ideas without more information. As always, you have to be sure the system is fully charged with refrigerant before diagnosing anything else. Then visually check if the compressor is engaged or not when the cool air quits.