95 Chev 1500 heater doesnt work

Ok so for quite awhile my truck has had heater probs. For the past 6 months the heater didn't even get warm. I have had the blower motor replaced and the switch in the dash replaced. After going over other threads in this forum I replaced the heater resistor and relay (behind the glove box) as well as the fuse under the hood. Now the heater works. It works so well that it doesn't turn off. The motor blows and the defroster works but now I can't get it to quit! Everything that has to do with the heater has been replaced except the heater control assembly in the dash. Any comments or ideas?