Let me apologize now if this post seems long, but know I'm only trying to be clear and give any information I know in hopes of narrowing this down quickly.

An 81y/o friend has a 2005 F150 XL which has a weird problem to me and he's unable to work on it himself. I've been checking what I know how, but won't simply start changing parts until I think I've at least found something that makes sense so any and all information would be accepted.

A few months ago, his heat stopped working.

It's not overheating or overcooling, with the gauge reading exactly as it should as to engine temp. This, to my amount of knowledge would remove the thermostat from being the problem since if it was "stuck closed" it would overheat and if it was "stuck open" water flow would eventually provide at least a small amount of heat on any given day.

All ***** and "doors" are working and moving correctly.

Antifreeze flows through the inlet and outlet sides of the heater core, but *only when it's a warm day...On a cold day, the hose from the heater core on the passenger side never gets warm. And *there's the problem: only gets heat when it's a beautiful day like the "air flow" temp appears to match the ambient temperatures.

That's all I've really got right now. As said, any help to find the problem would be greatly appreciated.

 

Sounds like a plugged heater core to me

 

Thank you for your fast reply.

I also leaned toward the heater core, or at least the hoses. But if you're able, could you let me know why this would stop the flow according to ambient temp. That's the part that's confusing me because I'm left thinking that if it's clogged, it wouldn't "unclog" at warm temps,...Or would it?

 

They way you made it sound was that it would be a sign warm as it was outside.

So on cold days the hose was cold and on warm days the hose was as warm as the outside air?

 

That's *exactly what it's been doing... And not just cold on cold days, hot on hot, but full heat on hot days and just cold air on cold days.

I fully flushed the system today and then, separately, flushed the heater core until clear. I filled it with fresh antifreeze. No change at all.

Now I'm down to wondering about a problem with the "heater control valve"...? It's only mentioned in one sentence in the manual I've got and I've had no luck searching info on it. I'm just thinking that since all else has checked out, maybe there's a sensor or such that's malfunctioning and telling the system/computer (?) it needs more cool air. When I put on the a/c, the heater control button on the dash does get icy for the cold side and slightly warmer when set to the red, but in no way like "heat".

Nope, I'm no mechanic. Just thinking out loud and hoping someone will know of something else I can check.

Thanks for the reply. It'll be a long day tomorrow at work and maybe a long week, but I'll check in as much as I can for any replies received as well as if the problem gets fixed and share that info. Thanks again.

 

Are you sure the blend boor is working.. very common problem on 04-08

 

Thank you for replying. I haven't pulled the dash out to physically watch it. But I hear movement and all vents work appropriately when the button to switch blend is moved (feet, feet and face, feet and defrost...). Please let me know if there is another way I should verify this.

 

The blend door is used to blend hot and cold air. It has nothing to do with changing from defrost, to floor, to panel, ect. I would check the blend door for proper operation.

 

There's 2 blend doors. (Actually 3 I think...) One for vent selection, one for recirc or max AC, and one for temp which is the one TR is referring to.

 

If you have hot flow through the core which you said you did.. it has to be the temp blend door.