YAHP-Yet Another Heater Problem

[mcompton1973]

ok, I did a search, and I am not sure that my prob is a blend door problem. Maybe something else. Here is the deal. When I turn the heater to High Heat, and full blast fan after the truck has been sitting a while (like first thing in the morning, or when leaving work) it will start to get warm inside, and then for some reason it will start blowing out really cold air...it will do this for a couple minutes, and then back to heat. It may do this once or twice, but then the heat will work fine. It seams like it might be going cold on me if I get stuck at a stop light, and then start warming up again after I get going a little bit....but I am not sure of that. it only happens a couple of times a day, so proving that therory is tough.

I thought blend door was just all the time cold. What else could it be? any ideas?

thanks.

 

[stubborn1]

Sounds like a stuck thermostat to me.

Does your coolant temp gauge move up and down when the air goes from hot to cold?

 

[mcompton1973]

I have not noticed it moving up and down with the heat failing on me....
but I do know that the temp gage does move some. I noticed yesterday while warming up the truck that the temp got fairly warm, and then dropped pretty rapidly.....but I dont know that it coincided with the heater seeming to quit.

 

[TPLYNCH]

Another thing to consider is vacuum. The blend door is moved by vacuum. If for some reason you are losing vacuum, the door may move back to cold, and when you build up enough vacuum, go back to heat. If it happens at idle, it may be your not producing enough vacuum pressure...

 

[mcompton1973]

ok, I watched it when I went to lunch, and the thermostat appeared to be staying steady even while the heat dropped off....so maybe the vacuum idea is the problem. How can I check that and or fix it.

 

[mcompton1973]

bump

 

[Eneurb]

The temperature blend door is electric, not vacuum. I'd suspect a broken blend door.

 

[TPLYNCH]

Do you have the automatic climate control option?

 

[mcompton1973]

I do not have EATC climate controll, just the regular knobs.