I have a 98 f-150 with 133,000 miles and this is my problem. My truck is blowing hot air when i switch it from heat to cold. I thought it was the switch so i replaced it and thats not it,i checked the **** for cracks but it is fine. What could this be a presure line and the door is not opening for cold air. I dont have a clue please help. Thanks!

 

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I have the same problem with my truck, take a look at the fuse for the temp control. It also controls the reverse lights, ac clutch, cruise control, and temp control. It is in the fuse box in the cab. If the rest of your things I listed above still work then the fuse is not the problem and I am not sure whats wrong then. Sorry.. Also I have replaced the fuse time after time and have yet to figure out whys its shorting out, but I htnik it has something to do with my reverse lights. Good luck on your project.

 

Checked the fuse and its fine too.

 

half of the heater system is vacuum operated and the rest is electric operated. if you change the right **** from defrost to floor to panel and the air comes out those locations, then the vacuum is correct. if at any position you can move the heat **** from cold to hot and it is same temp then that is an electric problme. there is a mixing door down above the transmission hump that is controlled by an electric motor. the door moves and mixes hot air from the heater with cold air from outside to get a set temperature. if the doors motor is bad, or switch that you replaced is bad, then the temp is always the same, either hot or cold. i dont know the exact location of the motor, but you might lay on the drivers side floor and look toward the center of the truck from the gas pedal. you should see 4 electric wires that come from the switch you replaced. i would also check that there is power to the switch (probably a red wire?) and that the fuse is o.k. that supplys the power. if you got 12 volts to the switch and switch is o.k., then the motor is toast.

 

Hopefully, it isn't the blend door......

..but it probably is.

Steve

 

how much are those

 

The part is cheap. The labor isn't.

It would be a good idea to get a definitive diagnosis before just jumping into that job. There are other possibilities that could also cause this issue but the blend door is one of the more common ones.

Steve

 

i am having the same problem but i have electronic climate control. Sounds like Steve(ill) really knows what he is talking about. I need to examine the system a little further. Do you know if the system for a 1999 navigator is the same as the 98 f-150?

 

Pretty much the same...

Steve

 

the blend door and motor operator are both buried in the dash behind the radio. takes all day to get the dash out for access to the door and motor.

 

thanks for the info I will let you know how it goes.