560 sec climate control, potentiometer
 

Hello! I installed a new monovalve in my 91 560 SEC due to lack of heat, and now all I have is heat. I checked the DC voltage at the monovalve connection, and it remains at around 13.4V no matter when the temp wheel is turned. Does this mean my climate control unit is shot? All of the buttons do what they are supposed to do, but blow strictly hot air... The AC was working, not sure if hot air is now getting into that flow, too... also, no instrument cluster or console illumination. I have the potentiometer out and am ready to replace it, but could there be some other problem? All fuses under the hood are good -- but is there another fuse that controls those lights hidden somewhere inside the car? Perhaps a control module of some kind? Is there a way to meter the three pins on the back of the instrument cluster that the potentiometer fit on? Can I test the potentiometer outside of the car? I apologize for all the questions, but that about covers it.
Thanks in advance, Bill Hard in NJ.

IIRC, the Klima unit should pulse the monovalve unless you put the temp dial all the way hot until it clicks, at which point the monovalve should get a constant voltage and stays open.

If you're getting constant voltage at the monovalve, the likely culprits would be either the temp dial or the Klima unit itself.

For now you can disconnect the wire to the monovalve and that will cool things down a bit for you.

Bill, there is a fuse behind the cluster in 126.045 cars up to serial num 491584. Not sure what model years that covers, but if yours is included, the fuse plugs into the back of the oil pressure/fuel/water temp gauge on the left side of the cluster. Part num is 201-546-00-25.

Sorry to drag up this old post, but I wanted to correct a mistake of mine. Apparently, my assumptions about when the monovalve should and shouldn't be getting voltage was incorrect. I had assumed 12V = Open, but I have seen another post which directly contradicts that assumption......

I'll have to go stick a meter on mine to be sure......