Can't get hot air. A/C works great. Checked heater core...in/out both hot. Checked core itself, plenty warm. Checked blend door...goes all the way open and shut (using the air temp switch). Checked other door (vacuum) that diverts air to floor or defrost...works perfectly. It is as though the air isn't flowing through the heater core, but only across the face of it....how can this be? Any thoughts/help would be appreciated.

signed,
will need this fixed soon, as it's gettin' cooler.

 

Is it a stock heater core or a replacement? I have found that none of the non Ford reproductions work. They're a little small and all the air flows around them. I spent hours and 2 heater cores finding this out and it sounds like you've got the exact same situation... It drove me nuts thinking about how air could pass through the system and not get hot...

Right now I have the heater box cover off and a rag stuffed around the core to make the air go through it. Leave the box cover off and it blows directly into the cab. Good jimmy rig to keep me toasty for now...

My next course is to silicone around the sides of the core that are close to the box and seal those sides. Then I have to bend up a small piece of stainless and JB weld ( I would weld it but taking the core loose a third time is more than I can bear. JB is good for a sustained temp of 500F ) it to the left side of the core near the temp blend door. If you bend the stainless properly and take your time JB welding it to the core it should work just fine and still allow the heat / cold blend door to operate properly... I'm gonna make a photo documentary of this process next week when I do it and post it up .

Or you could just buy a Ford heater core...

 

It is a stock core, I assume, as it was a very well kept one owner has 155,000 miles on it now. What still baffles me is why, if the core is warm/hot, why is the air blowing not hot?

 

Flow through the air box doesn't mean flow through the core. If everything works and the components are in good working order, it's probably bypassing the core. Core hot doesn't accomplish anything without airflow through the core.

Try pulling the heater box cover and stuffing a rag tight around the core, warm it up, and turn on the fan. If it blows warm then you've got the same problem I did. It's a quick easy task. I've also heard of older cores (maybe if it's still the original) getting gunky and still flowing the coolant, but only through a few of the vanes. Heater lines get hot but the air flowing through the core doesn't get heated. Pulling the heater box, stuffing rag, and running the blower is a ligit test of this as well.

155k on it I wouldn't assume anything. Keeping up a vehicle well means they replaced what needed replacing... The stock heater cores are darker colored, kinda a brown-copper and there are 2 humps on the top and bottom. Repros are generally more silver / galvanized and tend to have flat tops and bottoms.

 

The core pic in this thread is a stock core.

https://www.f150forum.com/f10/heater-problem-120189/

 

thats my heater core, I have to change it though because the one in the pic is leaking

 

Thanks Winter T. I suspect, based on your description and the pics. in the thread, that mine is original. Will try to get to this in a few days.
Thanks again.

 

Just got my problem of barely warm air on the heater core fixed. Previous owner had re-attached heater hoses up backwards. Trust me....this matters a lot. We now have hot air blowing rather than luke warm air. I had even discussed this with a Genuine Ford Garage Mechanic and he didn't think there was an in/out difference. Guess one needs to learn some things on his own huh? I was about to decide the core was plugged. Hope this may help someone else.

 

I have a problem that's similar to S Jenner's on my '99 F150. My heat works fine for about 15 minutes....until the engine temp reaches normal, then I loose heat to the cabin. After the engine cools, the cycle repeats.

I'm suspecting the blend door/Actuator, but haven't done any troubleshooting. I need to figure out how to get the glove compartment door off first, I guess.

Any tips on where to start would be appreciated.