Thank's for taking the time to look at my post... i purchased my truck last summer and i was in the navy and on dyployment so i haven't got a chance to use the heat till recently and i relized it didn't work, then a few day's ago i was trying to defrost the wendshield "off road hitting bump's ect" and the heat just suddenly came on and it was werd because i had the thermostat on cold and the switch on defrost.... it worked great for about 2 day's and then it stopped working again... and every now and then when i'm going down the road i'll start playing with the controll's it will come on again but i'm not sure if it is because i'm playing with the controll's or because i'm hitting bump's.... i just took the hot/cold switch out and cleaned off the contact's and bent them out a little to make better contact but that didn't work... the blower work's fine, the vaccume lines and selector switch (ac/defrost/pannel/floor) all look good, so now i'm at a loss, they only thing i can think of is thier is something wrong with the wires on that hot/cold switch... if you have any idea's let me know i will try them out....

 

The hot/cold switch or rheostat as they are called are prone to going bad or having a crack in the backside of the **** which results in the inability to adjust the heat. Pull the **** off and check for crack(s) where the shaft goes into it. If the **** is good but appears to be very loose when moved, it is probably the rheostat, which means you need a new switch.

 

Michael,
Another couple of things could be causing this. The blend door actuator motor could be acting up. I used this thread https://www.f150online.com/forums/sh...ad.php?t=212548 to check mine out. It could also be that the blend door itself is broken which is what was wrong with my truck, I have a 1999 F-150 too. A broken blend door seems to be fairly common. When you have the actuator motor out you can use a mirror and flashlight to take a look at the point where the actuator motor and blend door come together to see if the blend door is cracked or broken. Mine looked cracked but it was actually broken into two pieces when I removed it. Quintin has written up an excellent piece on replacing the blend door in this HVAC forum titled Blend Door Replacement with Pictures. Hope this info helps you.

AlanT

 

the switch look's fine and so dose all the other wiring, is thier any way to check the blend door without taking everything apart ??? from all the thread's i have read on this and other websites this seam's to be the problem... so what dose this part do ??? where is it located ???how much of a pain in the *** is it to take out??? do i need this peace... i do not use the ac because i have a 6 inch suspension lift 4 inch bodie lift and 39 inch tires so i get about 8 or 9 miles to the gallon so i don't use the ac, can i just yank that door out and keep the heat working...ps thank's for the help...

 

You can remove the black cover on the transmission hump and peer through from the passenger's side to the blend door motor to see if the door is split. You'll see a motor with a white connector going to it, that's the blend door motor. Poking upwards from the motor is where it engages into the blend door. Move the temperature switch from hot to cold and look for splits. Here's a picture of a broken door removed from the plentum chamber:

 

4 inch body lift ??? There's your problem right there! My blend door was also just replaced, to the tune of $522 at the dealer . I tried for two days, using Quintin's instructions and the Haynes manual and couldn't figure it out. The top of my door wasn't cracked tho, it was gooooone. It is very much a pain in the *** to get out, figure at least an entire day or two. Eventually on mine it got so bad that if I hit the brakes, the door would swing shut and I would get cold air. If I would hit the gas it would swing open and I would get heat, however, it never gave me the temperature I wanted, it was always the opposite.

 

i would have to say it is stuck in the cold position because that is all that comes out... is there any way to lock it in the hot position i could care less if it blew out cold air i'll just turn it on till i get warm then turn it off...

 

When I was testing my actuator to see if it works(had the ignition on and the actuator motor out)It immediately went to heat without the actuator in.I wasnt getting heat at all before I pulled it out so you could try that.Heres a link that i followed to replace mine. https://www.f150online.com/forums/showthread.php?t=212548

 

ok cool thank's for all the help i've just got off work and i'm gonna go yank that peace of **** outta there i'll tell ya how it work's out

 

WOW what a pain in the ***.... i pulled the black trim cover and i found the actuator and it worked fine and i broke out that little section of floor vent underneath the actuator(no one can see it who cares) un bolted the actuator and a bunch of what looked like to be ground up plastic fell out and i stuck a screw driver up there and jammed the door open and i took a zip tie and zipped the screw driver in place so the door couldn't swing back shut and now i have heat... so in other word's you can go to the dealer and pay $550.00 or you can get a few beer's and send in the redneck to jerry rig it... thank's for all the help it's verry much apreciated...