I just bought a 1997 f-150 and the heat only blows warm. if you turn the control all the way up, it blows cold until you turn it just a touch back. Any ideas how to fix this? The radiator fluid is ok it was a little low, but I filled it. no leaks that I can find. I thought about replacing the core, but I have never done this before and am not sure if I should attempt it.

 

Welcome to the site, now lets ask a couple of questions. Does the engine read normal engine temperature? Are both heater hoses the same temperature as the upper radiator hose? If both answers are yes than the system appears to be working properly and the problem is inside the cabins plenum chamber. There is a blend door to mix cold air with heated air. This could be out of adjustment if its a mechanical cable or perhaps a vaccuum leak if vaccuum operated.

 

The engine heat show normal, I have not check to see if both hose are the same temp. After it is running for 40 minutes it does blow warmer air, but if you adjust the temp ****, it starts to blow cold again. Then I have to jiggle the **** to get warm to blow again. This truck does have 213000 miles on it, but has been kept in great condition. I am not sure when the last time the cooling system was flushed.

 

I had a proplem like yours once, the **** was broken and even though I turned it back and forth to adjust the temp it barely affected the temp. Bought a new **** and fixed the prob! You probably won't be that luckey, but check it out.

 

Had to replace my blend door actuator for pretty much the same symptoms. Didn't cost much, but sure was awkward to get at.

 

I have ten days off starting next week. I guess I'll tear into the dash, and see what I find. I use to install car radios, so it shouldn't be to hard. Thanks for the suggestions.

 

If you have a good dealer near you, I would suggest talking to the guy at the parts counter. They have heard a lot of war stories usually and can help you to diagnose the problem. I always hate it when you tear something down and can't find the fault. Good luck.