Heater control knob or blend door actuator?
 

I have a 98' F150 with 127.5 k miles, so I know things now will start breaking more so than in the past. I have a problem with the heater heat/cold not working when I swith it to cold from hot, it stays on the hot side, or the opposite. I read the thread on the blend door acuator on the newer fords, and wanted to know how you know if it's a blend door actuator or a hot/cold switch on the controls. If anyone with a similar year had a similar problem let me know.

:coffee:

My 1999 F-150 has had similar problems. The rear of the temperature knob is a hollow shaft (Female) with a metal insert. This mates with the (Male) shaft of a potentiometer, which controls voltage to the blend door. The (Female) shaft is proned to split which prevents the metal insert to remain stationary on the (Male) shaft as the temperature knob is rotated (similar to freewheeling.) Thus, say you had it set on heat, but wanted a little cooler and you rotate the temp knob to the left. The temp stays the same. Another example: say you have it in heat with the temp knob all the way to the right. You have hot air. Now select the A/C side and rotate the temp knob all the way left. You expect cold air, but you will get only heat because of the faulty temp knob.

I first had these problems about 3 years ago. I tried gluing faulty knob and switched it with the Heat/AC select knob putting the best knob on the temp control. Things went good for a while, maybe a season or so. Begin to have similar problems again. Removing the temp knob and spraying that area with electronic cleaner seemed to be a solution. But what was happening was the good knob (the unglued one) had followed her sister and had split. I did not find this out at first.

I figured a bad potentiometer. So I disconnected the negative terminal from the battery and easily popped off the dash trim piece around the radio and HVAC control. Four screws hold the HVAC part in place below the radio; a (9/32) socket and/or wrench is used to remove. The potentiometer is held in place with one screw (use 1/4" wrench to remove.) There are 3 pins (L M R) on the potentiometer. With the shaft from the pot set to hot extreme I got these resistances: L-R 5 ohms, L-M 4.7 ohms and M-R .3 ohms; turning the shaft to cold extreme: L-R 5 ohms, L-M .3 ohms and M-R 4.7 ohms. I figured potentiometer was okay and it had to be a split shaft behind the knob and not holding the metal insert in place. I used 5 minute clear epoxy with which I have been having good luck. Before I put all back together I reconnected the battery terminal, set the pot shaft with a pair of pliers (I had the metal insert) on the shaft. It worked thru a full rotation, because the pliers did not slip on the metal insert.

Taking it to a Ford dealer could have cost well over a $100 and probably a lot more. I guess Ford expects us to replace our poorly under rated knobs at no telling what price. I'm guessing ~ $8-10 bucks.

I know that this post is a year and a half old or so, but I registered simply to thank you for mentioning the KN-OB! I had purchased a second actuator and replaced the ld with the new and i had the same problem and I was totally stumped. It had not occurred to me that that kn ob would be a failure point. Its my girlfriends truck and she tells me after the fact... "oh yeah honey Im sorry that was the problem before and I had it fixed so I didnt think to mention it to you... :confused:" We have been dealing with a non working heater for months!