Symptoms: AC stuck on hot... yuck!

After reading numerous threads on this topic, I was positive I had a broken blend door. However, I have removed the blend door motor, aka actuator, and made some interesting discoveries. With is still connected to the wire harness, I turn on the air and move the temperture contoll ****. THE ARM DOESN'T MOVE! No problem, the motor is broken... so I thought.

I took the cover off the actuator and a multi-meter showed 12.5 V was getting to the back of the harness.

A side note: The wire harness contains 5 wires. 2 for power and 3 that go to a potentiometer on the control panel (The **** that controlls the temperature blend).

Now the funny part. I took the actuator out and connecting a 12 V DC power supply to the two power leads (leaving the control wires open). The motor now turns the blend door arm!

This leads me to believe there is something wrong with the potentiometer that varies the 3 control leads. Can someone with a little more knowledge let me know what they think, before I go buying parts. Thanks! (I have some pictures, but it looks like they removed the file attachment part)

 

I haven't delved in as far as you have, but it sounds like we might be having similar problems. My symptoms:

I have blown 4 potentiometers in around 10K miles. It's not that they're blown electrically, but that after awhile the potentiometer loses all resistance and it I can't change the temperature. Every time I replace the potentiometer, it fixes for awhile and then dies again.

Called the service manager at the local Ford dealer, he has never heard of this before. I was about to buy just a standard rheostat and solder it in there, but the NAPA guy said that was a bad idea. Something about it could blow the blend door motor. He also suggested checking the motor and the potentiometer and seeing if there was a short somewhere seeing as those are the only things in the circuit.

Has anyone else out there had this issue; and better yet, fixed it? Any help would greatly be appreciated

 

Hi Guys, I am also having a similiar problem with no luck finding a cure. I did replace the BDA. It worked for about 5 seconds and hasn't worked since. If either of you have had any success, please let me know. I plan on looking for damaged wiring Sat monring.

 

I also have the same problem. I've changed the Blend door actuator and the motor makes noises, but doesn't move. The temperature switch doesn't move smoothly, so I'm guessing my problem is there, I don't really feel like taking my dash apart any more that I have already. I'm wondering if I can hook up an external rod to move the blend door on the shaft?

 

A potentiometer is just an electrical resistor with a wiper attached. The wiper is attached to an object such as the blend door in order to measure it's position by measuring the electrical resistance of the wiper. Measure the resistance across the potentiometer and then measure from one end to the wiper. That reading SHOULD be less than the first reading. If it's not,, then the wiper isn't making contact with the resistive element. That's a COMMON problem in potentiometers, particularly in cheaply and shoddily made ones that are used in automobiles. You can probably fix it by spraying some "Tuner cleaner" in it. If you don't know which connection is the wiper and which are the ends of the potentiometer, you should be able to find out by trial and error using an Ohm meter.

If you've ever had an old TV or radio that made a lot of noise and the volume control was "scratchy" then you've encountered the exact same problem with a noisy potentiometer.

You used to be able to buy tuner cleaner in HD but I doubt that they carry it any longer. Look for it at an electronic (not electrical!) supply house or ask at an electronics repair shop.

You can also check the potentiometer by measuring the voltage on each pin when the vehicle is turned on. One pin will probably read 0 volts and will be connected to battery ground. One other pin will have a constant voltage on it, probably about 12 VDC and the third pin will be attached to the wiper and should vary in between the first two voltages. The voltage on that pin should be proportional to the position of the blend door. If the wiper contact is dirty then the wiper voltage will probably jump around erratically or just remain at a constant voltage regardless of the door position.

 

Electrical contact cleaner that you can buy anywhere should work fine, just make sure it says it's non-residue.