Baffled by no heat!!
 

Hey all,

I have a 97 F150 4X4 4.6l V8...I have no heat at all...blows ice cold air...

So far, I checked flow through heater core, and no restrictions, blend door operates fine...changed out the thermostat, and still no heat. Once I took the cap off the pressure reservoir and put on a pressure pump to get rid of air bubbles, I got heat...110 degrees worth. But when I removed the pressure pump, the heat went away. I even disconnected the a/c compressor just to ensure it wasn't overriding the heater....ice cold air!!?? I'm baffled...I don't mind the cold, cause I'm a fat boy...but I can't defrost my windows to see where I am going. Any ideas, please throw them at me...I appreciate your help!! Thank you very much!!:-X15

Double check the thermostat, and ensure your heater core is not "plugged"

is your truck temp heating up?

Not heating up, but it must be the blend door....sitting at idle I get heat...once I start driving, it gets ice cold.

Take the finish cover off the floor vent in the center, drill a 3 inch hole with a hole saw, you watch your blender door move or not, usually the pivot breaks off the door, quick fix, run a screw into the hindge either for the heat or cold depending on which way you move the door, kinda rough solution but works, tape the hole with good aluminum duct tape, replace finish cover

Sounds much easier than removing the dash!! I have one question...can I get to the recirculator door behind the glove box? If I shut that, would that keep the cold air from coming in as well?? Or should I just cut the 3" hole in the plenum by the blend door, and go that route instead? Thank you guys very much for your help, I truly appreciate it!!:-drink

OK...completely baffled now!!! I cut a hole above the actuator for the blend door, held a flashlight by the whole, and turned the temperature knob...and the door works fine!!:'( So now what?? As long as the truck sits still, I have heat...as soon as I start driving...cold air...I'm at a loss!!:confused:

Sounds like you have a big vacuum leak to me. Spray some carb cleaner around the vacuum lines while the engine is idling and listen to see if the engine rpms go up. Usually that is only when you are on the skinny pedal, but if you had a big one that would add up. The resevoir is behind the battery box, toward the fender.

I'll give it a shot!! Right now, I'll try just about anything!! Someone told me to check my fan clutch...said I may be "overcooling"?? Didn't think that was possible, but my heater hoses are always hot!

If it's a vacuum leak, the airflow doesn't change temperature, it just redirects to the defroster outlets.

If the outlet air changes temperature when stopping or starting, it's usually the temperature blend door flopping around.

OK, well that blows that theory out of the water...My blend door works nicely...I even pushed on it once it moved to the heat position, just to make sure it wasn't flopping, and it was good and tight...

This sucks...I don't know what it could be...it's baffling the crap out of me...I appreciate everyones help...like I said, I'll try anything...I just wanna see where I'm going on cold mornings...

Well like the earlier post if your ac or defroster is on cold be freezing the coil up solid and losing air flow not sure how its set up but mks sense, ck your freon level

Is your anti freeze at a 50/50 mix and not way to thick, clutch on your radiator fan working properly ?

I unplugged my AC compressor last weekend, and it's been unplugged ever since, just so I know it would be that...I don't know if the fan clutch is bad or not? But I do know that when I pull in my driveway and it's blowing cold air, I jumped out quick to feel my heater hoses, and they are very hot...both of them...

Who knows...I might just say screw it, and buy one of them ceramic heaters...LOL:-X16

That sure sounds like a heater core that has plenty of hot coolant going through it very nicely, but with no AIR FLOW to remove and distribute the heat.

Any chance you could get someone to take over driving it once its well warmed-up, while you check that blend door position while cruising along?
Oh yeah, remember to wear your seat belt, too :-X18