My heater control valve solenoid gets power (pod activates and valve closes) when the climate control is off, and the solenoid loses power (valve opens) when the climate control is switched on, no matter where the temperature slider is--even on the coldest setting with the little micro switch pushed in.

I know it's not the inside temperature sensor, b/c I checked it with an ohm meter and the resistance varies if I blow through the vent.

I know it's not a vacuum leak, because the problem originates upstream when the solenoid loses power from the climate control head.

I know it's not the climate control head, because this is a rebuilt unit from 928 Int'l (I thought it was my old head). At least, this is very unlikely.

Except for the external sensor, which I can check, are there any other sensors that provide feedback? Is the calculation/comparison of inside vs. outside temperature made by the climate control head?

 

You've got it. There is an internal and an external temp sensor. That's it. You should be able to check to see if you are getting a reading from the outside temp sensor up at the control/head unit. My guess is that you are not getting a reading, i.e. there is a short. Because when the inside temp is lower than the outside, it mixes/defaults to heat. With an open outside temp sensor, the reading is infinity, so you would get full heat.

If you have no reading for the outside temp sensor at the head unit, you need to start doing some investigation. The outside temp sensor is located behind the front cover in the front driver's wheels well (under the head light). I'd check it here first, then start working back. I believe there is a connector (pass through) above the accelerator pedal, and then finally the head unit. You might also, be able to run a temporary direct connection from the outside temp sensor to the head unit to see if that remedies it.

Good luck.

 

Thanks. I heard you couldn't buy the ext. temp sensor anymore, but that it was a very simple device that wasn't much prone to failure, so I didn't bother digging around to make sure it was still there and operational. Sounds like that's the culprit.

Assuming I can return the head unit, and assuming I can find a good used replacement, this should be a much more inexpensive fix.

Thanks again for the thoughts. Anyone know which connectors/leads going into the climate control head are the inputs from the internal and external temp sensors? I'd like to make sure that the readings are making it all the way to the climate control head, and I don't have any workshop manuals.

 

Okay, well I crawled under the car today and tested the external temperature sensor. With my ohm meter set at 2k, the reading was somewhere around 429. I opened the hood, and as the sun hit the engine compartment, the reading started to climb. I'm in San Diego, and it was probably somewhere around 75 degrees at the time.

Everything I've read seems to suggest that these sensors don't malfunction (i.e. become miscalibrated) so much as quit working altogether. As long as the resistance changes as the temperature changes, chances are it's "right."

So I am left with three explanations: (1) The rebuild climate control head I bought has the exact same problem as my existing climate control head (improbable); (2) the readings from the internal and external sensors aren't making it to the head; or, (3) the internal or external sensors truly are "miscalibrated" so that the head is not making proper sense of them.

Can anyone help me out with respect to which wires/leads that connect to the climate control head actually represent the feeds from each sensor? Anyone with a schematic?

It seems like it will be a real PITA to track the wiring path from the external sensor, if that ends up being the problem. The internal would probably be fairly easy, although I don't really relish having the console out -again-.