We replaced the "push & play" unit in the dash because that was what the GM garage here said it was just to have the new part do the exact same thing. Totally cannot control the temperature. The fan works, the numbers display but when it failed to produce heat, the display now blinks the heat setting numbers, which it never did before. They don't seem to be able to figure it out at this garage. Please help.
Check to make sure the blend air door is functioning. It determines the air temp entering the vehicle. It is located near the heater core in the heater core box. If it is stuck or the actuator is bad, you won't be able to adjust temp.