AC temperature acuator noise

As you noticed, it is an electrically driven actuator; it also provides an electrical signal indicating its position as feedback to the A/C controller. When the controller wants a certain position, it will look at the position signal coming back from the actuator, and send a motion signal in the needed direction.

The position signal is probably generated with a variable resistance element, the same as in your accelerator pedal and steering gear. These variable resistors can get dirty/worn/oxide-coated and provide a position signal that isn't smooth or consistent. If the "position" signal is jumpy and noisy, the controller will be sending frantic motion signals one way and the other trying to compensate for what it sees as position errors. This A/C actuator is breaking you in gently so you will know what's happening if your accelerator or power steering ever do it.

Somebody else on the forum may have some details for disassembling the actuator. I have not done it myself, but if you can get any access to the resistance element, a magical fluid called Jiffy Bath that you can probably find at the local electronics shoppe works wonders for cleaning it up. Try shooting some in and working the actuator back and forth some.

Hope this helps,
-Chap

 

The position encoder is built into the actuator. You should find a five-wire connector plugged into it. If it's the actuator I'm thinking of, they are white-red, brown-yellow, yellow-red, blue, and brown-red. The controller sends a reference voltage across the first two, and reads position back on the third. Then if the position read back isn't what the controller wants, it sends a driving voltage of the needed polarity across the fourth and fifth wires until the position is right. Moving your temperature dial changes the position the controller wants, so it will then drive the servo until the indicated position matches.

If the indicated position coming back from the servo is a noisy signal, the controller will be busy continually futzing with it. That probably doesn't mean anything is wrong with the controller (which is, as you guessed, a circuit board hiding out behind the A/C controls on the dash).

You know, you might want to ask your controller if it has noticed any problem. Turn the key off and the fan switch off; turn the key on, tap the A/C button 3 times, then turn the fan to auto. If the lights just do a steady fast blink, the controller hasn't noticed anything to complain about. Otherwise count the blinks. You get a two digit code, something like blink ... blink blink blink for 13.

Just turn the key back off to get out of the blinky mode.

I wouldn't be surprised to get a 'normal' report (just fast blinks). Unless the signal from the servo goes really obviously wack, the controller is probably just going to keep responding to it by trying to correct the position, without necessarily logging a malfunction. But it's worth checking.

-Chap

 

I have this problem on my prius last year and I end up replace the acuator (the parts guy car a/c servo or something like that). After that it didn't jerk back and forth anymore. It just a 10 minute job and like you said it locate on the right side of the driver ankle.

 

I am having the same problem and the dealer told me after diagnosis that it is a servo motor and will cost about $500.00 to fix