I have an '01 Silverado that my dad bought new and I have owned for the passt 6 years. About 2-3 weeks ago my heat started to work intermitantly. After the truck warmed up it would work fine, then start blowing cool, then back to hot. Now, for the past 2 days I'm only getting cool air, which is inconvenient at best since I have an hour drive to work and temps were in the single digits this morning.

My temp gage is reading normal (just below 210). The coolant system has never been flushed. Could that be the issue? Any other thoughts?

 

I think it is probably the control head. You have a blend door inside the A/C / Heat plenum that switches from heat to cold - it basically just opens a door so the air now passes through the heater core before coming out of the vents. If you are getting intermitant heat that door is probably opening and closing which will be due to a false signal from the control head. Either that or a thermostat issue (possibly sticking causing the colder coolant in the radiator to be circulated through the heater core) are about the only things that can go wrong in a heater's system besides leaking.

 

Okay, so control head. Is that the actual control in the dash?

 

Yes it is.

 

The one thing shamrock forgot to mention is your heater hoses......with the truck fully warm put your hand on each heater hose going to the heater core if one is cold and one is hot then you have a plugged up heater core.... some trucks have a heater control valve also that likes to go bad which is in one of the heater core lines and controlled by vaccum

 

True, thanks for the correction.

 

Thanks guys. I'll see if I can figure it out this weekend.