Heat all the time... W126
 

In my 560, I only have full heat all the time... even with the AC running. So, checked the monovalve insert first and there are no tears in the diaphragm that I can see. I suppose I can replace it as they are only about $45.

What are my next steps to check out? I believe the push button unit to be original to the car, is it possible it is not sending power properly to the monovalve?

I would check first if the monovalve is working.
With a multimeter you can see if the coil is ok (or just put 12 volt to the pins).

Sometimes the (very small) wires from the coil to the pins break.

Rob

You should probably sell that 560SELoL to me.

Hm okay this is low on my list as the front end is trash, but I will take a brief peek when I start it up next month. :)



lol Wes. You stole that 300jestE from me. :D

I'm not very good at giving mechanical advice, but i had a similar thing happen to me. i disconnected the mononalve from the ac control unit in the dash and connected it straight to the fuse box. When the key is on the monvalve engages and I can still control the ac from the dash control. It is temporary but it was so hot here I had to do it. I dont know if that helps but I gave it a shot. Here is a link to the post I got much help with. http://www.peachparts.com/shopforum/diesel-discussion/280862-82-300td-ac-question-help.html

I had a similar problem, see my threadI believe your controller is similar to the W124.
1) Check your mono valve as advised
2) Check voltages at the connector when the knob is turned at both max and any middle settings.

I have to recheck the duovalve because I replaced it before testing. If not the valve, I suspect a bad knob rheostat at middle settings or bad cabin temp sensor as suggested.