I have a 1999 GMC Sierra. I'm having a problem with my heater. It will not switch between hot and cold. To make it switch I had to take off my kick plate and there's a wire clip that if I unplug it and then plug it back in it will switch. I have to do this every time to switch it back and forth. also its ether all the way hot or all the way cold, no in between.
Any help would be greatly appriciated.
Thanks.
Mike.
Foregot to metion that I did test my controll module. I took it out and tried it in my friends truck and it worked fine.

sounds like that actuator itself

Thanks.