Some days i get in and the ac works fine other days one side blows hot while the other blows cold and it switches sides

 

LLY: Ac blowing hot [Archive] - Duramax Diesels Forum

or

"It needs to recalibrate. Turn the ignition on. Wait about 20 seconds. Turn off the HVAC. Turn off the ignition. Wait 30 seconds. Start the truck. Wait antoher 15 seconds. Turn on the HVAC. It will recalibrate and be working within a minute!"

see if that does it for you

 

That works for a short while then it goes back to blowing hot