Hello-

The problem w/my California '85 300CD-T has been intermittent heat when the temperature wheel on the ACC unit inside the car has been turned to the max. (red) position.

This is the testing I did and the results:

1. Test condition: Engine running, wire to monovalve disconnected, ACC unit center button pushed and fan. at max. and temp. wheel at max. (red) position.
Result A: Heat at side vents (as expected).
Result B: 13.3 volts [batt. voltage] on monovalve wire (*NOT* as expected, should have been zero).

2. Test condition: Engine running, wire to monovalve connected, ACC unit center button pushed and fan. at max. and temp. wheel at max. (red) position.
Result A: Heat at side vents (as expected).
Result B: 13.3 volts [batt. voltage] on monovalve wire (*NOT* as expected, should have been zero).

3. Test condition: Engine running, wire to monovalve connected, ACC unit center button pushed and fan. at max. and temp. wheel at min. (blue) position.
Result A: Cool air from all four (two center, two side) console vents (as expected).
Result B: 13.3 volts [batt. voltage] on monovalve wire (as expected).

In short...
A: The voltage on the monovalve wire was 13.3 when the temp. wheel was at max. (red) or min. (blue). Suggests a failing ACC unit.
B: When the temp. wheel was at max. (red), and there was 13.3 volts on the monovalve wire, and the monovalve wire was connected to the monovalve, the monovalve was open and there was warm air coming out of the side vents!!! Odd because it seems like the 13.3 volts should close the monovalve and stop the hot water from entering the cabin.
C: When the temp. wheen was at min. (blue), and there was 13.3 volts on the monovalve wire, and the monovalve wire was connected to the monovalve, the monovalve was closed and there was cold air coming out of the side and center vents.

Anyone able to offer some insight as to what is causing these strange results?

Thanks-

Mike
Phoenix, Arizona

Monovalve has always +, the - connects thru the control circuit to close the walve.....

Sorry for my bad english im a Swede...

Try the EC button(second from right). Thats what I use for heat.

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'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles