Calibrate/adjust heater temperature controls?
 

Hello, I have a 2002 GMC Sierra. Ever since I bought the truck, the heater and air conditioner temperatures are out of whack. When turned completely to cold, the a/c works well. But just two clicks 'warmer' and it is actually too hot. Is there a way to adjust the temperature settings or calibrate it somehow?

Thanks in advance for any ideas or suggestions on this!