F350 heater blows cold air
 

My truck is operating at normal temps heater hoses are hot heater core is hot .all the switches are working as well as vac pumps to move doors .if you turn it to cold it will blow cold air when you turn it to hot it only blows barely warm air when switched to defroster it blows cold air . I can hear the doors moving inside boxes it switches to all heat functions just dont get hot on any of them .gets hottest on floor .books dont show me doors or what they do .any thoughts .thanks

I once had a vehicle with the wrong thermostat and the heat never worked, changed it out and viola, I had heat. Maybe you're having the same issue

check to make sure that your vac lines are pluged in ... under dash is the normal place i see them accidently unplugged ... other wise its most likley a vac cylinder... :tu:

i had this same problem in my 06 f250 here is what i did and a pic i toke that fixed my problem. the pic with show the location better than i can explain but on the passenger side in the engine bay there is a heater valve thing if you have it on your truck but there is a wire thing that was behind my valve that stopped the plunger from moving in and out and right when i moved the wire the heat worked perfect and a simple zip tie fixed it. also make sure that vacuum line is plugged into it and didnt fall. hope this works.

just click the pic to see!

What would you all do if the high, med, and low speeding for the air stopped working, as-in you had it on high then all of a sudden it turned to low and now that's all you have, I just replaced the plug in the back of the panel since it was burned to a crisp, and there's a new resistor in, but haven't checked it, maybe it's blown?:humm:

Itsnotapowerstroke, that could be half a dozen things such as you here the box switching placement however the doors aren't moving completely, more than likely its your thermostat however I'm not certified so yea best bet take it to a mechanic.

Sounds to me like the door that sends the air flow to the heater core isn't moving all the way, need to know if it's vacume or cable controlled. If there's something blocking the door from moving. Defrost should be colder if heat is warm due to the air runs through the ac to dry it before it gets warmed by the heater core, so if your dealing with Luke warm air that gets cooled by the ac when in defrost, it would be cooler. Since you said your running at normal operating temp and you feel the heater core getting hot.

Core could also just be plugged ... Seen it a million times . always fun too ...lol