W124(2.5D) with No Heat

[lpozzo]

I have a 1990 W124 2.5 Turbo Diesel with 160K miles and I have no heat. If I turn the temperature dial all the way below 65 degress, the air condition does kick on. I have no heat between 65 - 85 degrees at all. Eventually, once the engine heats up past 80 degrees C, and the dial is past 85 degrees (max), minimal heat comes out.

I conducted some tests with a voltmeter at the monovalve connector end and got the following results:

- With the car on and the CCU all OFF, I got 12 volts from the monovalve connector
- With the CCU on EC setting and temperature past 85 degrees in the click-stop position, I got .37 Volts
- With the CCU on EC setting and temperature past 65 degrees in the click-stop position, I got 13 Volts
- With the CCU on EC setting and temperature around 75 degrees, I got constant 13 Volts
- All the blower speeds work

Any thoughts what the problem could be? I appreciate your help. Thanks.