So the HVAC switch for my 97 Sierra started blowing air only at the ground. So, I went to the junkyard and picked up an HVAC switch that came off of a Tahoe with the rear defrost option. I hooked it up and everything work great. But, my mechanic mentioned to me that the A/C is constantly running even if the switch is turned off. Everytime the trucks is on, the A/C is on. Could the new Tahoe HVAC switch be doing this?