Temp control -> heating valve voltage

[kungfooren]

Hi all,

I'm troubleshooting my car is constantly blowing hot air. I took the dash apart and have located the internals of the temp control knob. I can see that the knob is connected to a cable which mechanically operates some flaps. That part looks ok. I probed the two electrical contacts on the knob by measuring the electrical resistance and found that it acts like a switch (10% of the range (cold) gives a closed circuit and the other 90% (warm-hot) is open circuit).

Issues:
I disconnected the two wire harness connected to the heater control valve by the footwell and the voltage always reads 0V no matter what position I turn the temp control valve. It's supposed to be 12V when knob is cold and 0V when knob warm-hot. Strange considering my knob is correctly acting like a switch. Why is the voltage always 0V at the heater valve?

Thoughts:
1) There may be some kind of short to ground somewhere which is forcing everything to 0V

2) 12V is broken somewhere


Help:
Does anyone have any experience with this? I measured the voltage at the contacts on the temp knob and it always reads 0V so even if it's acting like a switch, it's just switching between 0V and 0V. Should it be reading 12V or maybe 5V for a relay?

Thanks for any suggestions/links/photos/etc...

-jeff

[jlevie]

It sounds like there is a wiring fault that is not providing power to the temperature control. It is just a switch and the temperature is regulated by the blend doors in the HVAC unit.

[kungfooren]

Thanks. I figured it was a wiring issue. Looked at it again this morning and it seems something is still off. My 12V is apparently shorted to ground :(


I also found these which may be useful for anyone else facing a similar issue.

http://shark.armchair.mb.ca/~dave/BMW/e30/

http://www.bmwcabrioe30.it/utilityweb/schemi%20elettrici.pdf

http://www.e30tech.com/forum/showthread.php?t=103864 -- wish there was a higher resolution version

[jlevie]

Use the ETM for your car from http://wedophones.com/BMWManualsLead.htm

[kungfooren]

Thanks!

Turns out there is a 2A in-line fuse between the temp knob connector and the heater valve (solenoid). I replaced it and now I have the proper voltage. Unfortunately, my heater valve looks like it's busted. lol.