I own a 1998 F-150. I have had problems with the heat/A-C system for several months. Took it to two different mechanics. Cooling system flushed - thermostat replaced, etc. Worked better for a couple of days, then failed again each time.

Reading on this forum was very enlightening. Learned that I most likely have a blend door issue in the heater plenum. OK - I watched the heatertreater video and I can do that repair.

Question - is it possible to secure the door in the max heat position until I have the parts and the time to do the repair? Thanks for any help you can provide.

 

You can cut Heather plenum and make kind of doors just you should be carrefuly where you cut. Then wire blend door to something.
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I can't help but ask, is that blend door your talking about under the radio, I am having the same problem ,I can not get heat, or A/C.. Please advice soon , no snow yet .but its coming ,, thank you Scott

 

the blend door , gearbox and motor are under the radio above the transmission hump. YOu can remove the plastic lower dash panels and see it. You can then run it and see what happens. I have not done it, but others have said it can be removed - leaving the dash in, but difficult. I think you could wire or wedge it into one position .

 

if you lay on the drivers side floor, look above the gas pedal, over toward the radio... you can see the drive motor and wire harness.

 

I just read another thread that said above the heater core,behind the glove box there is an actuator, on the top of it if you can get to it , there is a 1/4" square shaped hole that can be used to adjust the door ,, does this make sense ? I am sure going to look at it this morning , Scott

 

Were you able to find any such thing?

I also have lukewarm heat. I did find the one blend door for the panel airflow but could not find the hot/cold blend door.

I took apart the hot/cold temp switch (from under the radio) and manually turned it back n forth but temp will not get hotter.

My temp gauge reads below 1/2, is this normal? The truck is originally from Miami, is it possible for it to have a cooler thermostat? im thinking out loud here.

 

I checked all the hoses while at operating temp. They all feel lukewarm, same as the air coming out of heater.

 

I found after searching underneath the dash, you can remove the glove box door.. There are two stops on each side near the top, on the sides, you have to pull the sides of the box toward the center , then the box will fall down. Now you can see a flat cover, I think it have 6-8 screws in it, the cover is maybe 8 x 8 inches, pull it off by raising it up the n angle the bottom toward you then down behind the clove box. Inside on the left is the blend door. Try to move it slowly start the truck let the heat go where you want it by moving the door, keep in mind the dial for temperature should be on hot. You can also control the temp with the dial, like halfway , or whatever, I live in Prescott, so I have mine cranked all the way to hot. Now , on the top of the heat box area , up the front of the heater and in line with the hinged part of the blend door on top , just eyeball this and at the very top of the entire box you will see a white part , about 1/2 inch high on the right side of it there is a small 1/4 inch , or so vertical shaft , now only about 3/4" is visual, but its enough to grab it gently with small vise grips and twist back and forth, only do this while you are moving the blend door at the same time, if they move together, the gears on the inside of that white gearbox are good. Ready for round two ??? Now with everything visable and a real good flash light(led) preferred , turn the temp control on your dash one wat of the other, while looking at the blend door confirm that they are , or not working in sequence. Truck must be running. If the dial on the heat temp works ok, but the door does not move, then its time the the thrid , and last round , and a little prayer would'nt hurt either. Back to the white box at the top , and to the small shaft on the right side that is vertical, and kinda in line with the hinged area of the blendd door , from the vertical shaft , go to the left of the shaft maybe an inch to the body , or housing of the white gearbox , about a 1/2" from the right edge take an ice pick and make a hole the same size as the little piece of tubing that comes with almost all rattle can lubricants , and carburetor cleaner, an 1/8" hole should work get a good silicone libricant , attach the little red extension to it and carefully slip the extension into the little hole , and while moving it from left to right, mostly right a little , give it a couple goo shots , and start moving the blend door at the same time as you move the temp control from cold (blue) to hot ,, at this point it would be better to have someone moveing the dash control so you can view the door, and the small vertical shaft at the same time.. Good luck , mine is still a little sticky ,but it does work now,, Scott