The heater on my '99 F-150 Supercab works very intermittently. With the temperature guage at normal operating range, the heater blows cold air. The heater core hoses are both hot. At first, if I pulled over and shut the engine off for a few minutes and restarted it, the heater would work normally. Now, it blows cold more often than not. Periodically it will work normally. There are no signs of leakage or antifreeze smells (heater core) and the engine operates at normal temperature level (doesn't overheat). Would a coolant flush help? Thermostat? Has anyone else experienced this problem? If so, what's the fix? Oh, by the way, it has 4.2l V6.

 

Your Temp **** is stripped. It will grab sometimes and other times it won't.

 

Left work the other morning and couldnt defrost my windows due to the heat not working. Sitting at work tonight and found this website. Read about the problems with the ***** so I ran out and checked it. Sure enough the **** was cracked. Man am I relieved!!!! Guess I will get to be in the treestand tomorrow. Thanks!!!!

 

the **** on mine is good. Any other hints? Cold all the time. Heater hoses are hot. Fan works good, I can direct the air up, down, and dash. Just no heat. 99 v6

 

If the **** is good is there a poss. that the blend door the **** operates is broken?

 

Yep.

Steve

 

What is involved for checking for a broken door? This is an electric setup, **** to door, is it not? I don't hear any noises when I move the ****, to indicate loose parts, etc.
No fuses blown.

 

I guess what I'm asking is, does the **** connect by cable or wires? And if the heater ducting has to come out, is there any hidden screws, or helpfull hints to this job? Interior dash work is my least favorite job in the world! lol

 

Still experiencing intermittent heating problems. A "new" twist is that when the heater is working, if you leave it on (in between driving trips) and don't shut it off, it seems to work for longer periods of time if that makes sense. This is real inconvenient in Missouri this time of year when it is 80 degrees one day and 35 degrees the next day. I'm leaning toward the blend door not opening all the time. Is there a way to check this without tearing half of the truck apart? ***** and controls appear to be good. I replaced the temperature control. Any info on the blend door and controls (vacuum) would be appreciated. Is there a good book or website?

Thanks,

Mechanically challenged Paige

 

Here is how the system works. The vacuum controls where the air comes out, upstairs, dash, floor. The heat temp control is 100% electric. The dash control, sends an electric signal down to the blend door, which has a servo motor/switch assembly mounted to it. In my case, the temp control, does change the position of the blend door motor/switch. So, at this point, with no heat and the motor moving, I assume the door is dissconnected from the motor, or the heater core is plugged.

Question: If the heater core were plugged, would the temp at both heater hoses be hot? Mine are warm to the touch. Absolutely no heat coming out, of the heater, what so ever.

 

I have a 99 F-150 that's having the same problem with no heat. My switch is good and heater core and hoses are fine. Blend door isn't damaged but is stuck in the "cold position." Is there a way to open it manually to get heat?

 

ttt

 

Yes both heater lines will be hot even if core is plugged. If you find that to be the case? You can take your lines loose and clamp your hose pipe on to it and blow it out. If that is the problem? After you blow it out you need to do a system flush and add fresh antifreeze.