A/C is not cooling. I turn off the ignition and a fan continues to run for 10 minutes with key removed and doors locked.
Have you checked for any debris on the AC condenser?
Gm has after boil circuit. Some of my gm rigs fans run after shutdown if ac was switched on at stop. I notice the fans don’t run if ac was off at shutdown.
this may give you some ideas where your problem is.
Car Fan Still On When Engine is Turned Off - YOUCANIC
I would guess a faulty coolant temperature sensor