01 4x4 silverado heater problem

Maybe it's the vacumn control behind the knob. Think those work on vacumn. Loose connection? Maybe the door is hung open to the heater core??? Good Luck, Pete

All the above, but even more likely the vac motor that opens and closes the heater/ac flaps has gone kaput. Usually have to pull the dash to get at those.

age

What year truck? On my 2000, I just fixed this problem by replacing the temp control actuator that controls the heater blend door. If this door does not close, you will have heat all the time. It is electrically operated and the one that usually fails is the lower center actuator. No need to remove the dash, just remove the "hush panel" below the dash for access. 4 or 5 bolts if I remember. You will find the hush panel direcrtly under the heater and you will be working from the inside of the vehicle. Dorman part at Kragen is around $50 and gm part at dealer around $95. I used the Dorman part 4 months ago and so far no problems. SF