1983 380 SEL
108 k miles
Cincinnati OH Weather mild lately 40 to 60
Only driven this car a few hundred miles, bought it a few months ago.

The symptoms:

When it was warmer and I ran the ac, it would freeze me out. Seems no matter where I set the temp wheel, the air just kept blowing cold. I would have to turn it off and back on to keep from freezing.

Now that it is getting colder I don't get any heat. The blower runs but no heat.

What I have done so far:
1. I replaced the control module (with the wheel and buttons etc) I had an extra one so I decided to try that. No change.
2. I checked the voltage at the monovalve. It has 12 volts steady on the hot and the ground cycles about every one or two seconds. I left the monovalve unplugged so no current would get to it and I get heat in the car, but he blower does not seem to kick down once the heat is up.
3. I checked the vacuum operated door behind the glove box and does open and close when the air is turned on and off. Seems slow but it does work.

What I think: Seems to me that the control module is not getting any feedback on the cabin temperature. I don't know how to test this.

Any help is appreciated.
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