Climate Control Diagnostics (electrical parts)

[Tom M'Guinn]

I've posted these charts on other boards, but thought they might be helpful to someone here someday. These charts summarize how to test the motors, sensors and solenoids for the climate control on the '85.5+ cars. If you are having issues, you should start with the basics -- heater control valve, heater rod clips, etc. But if all that checks out, it can be difficult to tell if the Climate Control module is bad (common) or if a sensor, motor, position sensor, or solenoid is bad (also common). These charts are based on the factory wiring diagrams and just make it a lot easier to test everything. If it all checks out and the system is still not responding as it should, then the climate control unit itself is probably bad. I'll try to upload all the pages here as jpegs, but they are also available as a single PDF here: https://www.carpokes.com/viewtopic.php?f=19&t=357

[Tom M'Guinn]

Also, here is a video showing how to use the charts...


https://www.youtube.com/watch?v=GjD0FqCNxIo&t=137s

[thomasryan]

nice

thanks for posting

[mikepellegrini]

Those are great charts, Tom. This stuff is really useful to me. I watched the video, it filled in the blanks on how to use the charts. Thanks Tom, for taking the time to do that.

I've been diagnosing a heat on all the time problem in my 86 951. I was driving one day last August (hot day, the heat was off) and suddenly the heat came on.

The plastic clip on the flap in the drivers footwell is good; you twist the temp dial and the mixing flap opens and closes properly.

The vacuum hose to the heater valve in the engine compartment appears to be good. The valve is open. The lever moves but returns to the open position once you release the lever.

Using your diagnostic charts, the other different flaps work ok.

The temperature sensors all read fairly close. After having run for 30-40 minutes, the outside sensor read 6.05K ohms, the inside sensor read 5.81K ohms, and the mixing chamber read 6.38K ohms (ambient temp in the garage was probably 75F. The air coming out the vents read as high as 119F when the car was running). Earlier when the car was cold (ambient on the car was probably 50F), they read similar, higher values.

The temperature regulation was always kinda spotty (set at maybe 70F, the temp would get really hot, then maybe after 20 minutes, it would cool down to the proper temperature). I unshipped the inside temp sensor - it was super icky, plugged up with dustbunnies. I cleaned it off and tested it. Fan runs good now.

I have good vacuum in the car at the solenoids (I think 15" Hg, measured off the supply side line going into the T fitting between the two valves). The impedance for the solenoids was within the range specified in your procedure (don't remember what precisely). But the solenoids don't operate at all.

I've tried two different control units that I believe work. The AC compressor comes on when you push the snowflake, and when you push defrost. And like I said the temp control dial works because the mixing chamber flap moves when you twist the dial.

How do I jump the solenoids to see if they work? I've put +12VDC to pins A3 and A4 (from your diagram) and nothing happens. Does that mean they both failed? I guess it's possible the recirculation solenoid could have failed without me noticing.

Does anyone know how do you get the solenoids unplugged? I've pried on the plastic caps and they don't want to come off. I don't want to ruin them.

[mikepellegrini]

I take that back. I turned off my space heater (which makes quite a racket) and now I hear faint clicks from each solenoid.

I have a pair from my spare HVAC unit. I pulled them and they also make faint clicks when powered. I hooked them up to a vacuum pump, and when energized, they let maybe 2 1/2 "Hg through, but that's it. That can't be enough to operate the heater valve is it? You can't see any travel in the solenoid rods.

[Tom M'Guinn]

You need to ground the solenoids (e.g., ground pin B4) then apply power to A3 and A4. Both solenoids have wires that run to a single connector mounted to the side a few inches away. That connector comes apart easier. I'd check the heater valve again. It might be leaking coolant past the valve even those the plunger seems to be in the right position. This site seemed down or I would have responded sooner, sorry, but you can always find me on carpokes.

[mikepellegrini]

Okay, thanks. I'll give that a whirl.

[mikepellegrini]

Got it. It was a vacuum leak between the solenoid and the heater valve.