a/c is blowing hot air on several occasions, took to dealership, they cant find anything wrong with it.
Out of warranty. Try an independent automotive HVAC shop.
Could be a blend door issue.
You are saying the ac works ok, produces cold air and then it does not produce cold air? Sounds like an intermittent problem. Work/no work vs working poorly all the time.
The next time it happens, see if the outside temperature displayed is incorrect on your instrument cluster. GM vehicles disable the A/C when the outside temperature is low. A failing ambient air temperature sensor can cause this issue.