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Old 02-10-2018, 06:05 PM
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Join Date: Nov 2006
Posts: 186
Monovalve wiring confusion

Last summer, I was getting hot air even when the A/C was on. I quickly learned that the mono valve wiring wasn't closing the valve when it should. I rigged a temporary fix by putting a ground wire to one side of the mono valve and a 12v power to the other mono valve wire that was giving power only when the ignition was turned on.

I'd like to make it work properly though. Both of the leads that connect to the monoV seem to be grounded even at when the mono valve should be closed such as when the A/C is on. Shouldn't one side be full 12v whenever the key is turned on and the other side be fully grounded when the A/C is on?

1984 300CD

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Old 02-10-2018, 06:44 PM
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Join Date: Sep 2004
Posts: 8,730
Originally Posted by gregp1962 View Post
... the mono valve should be closed such as when the A/C is on.
No. Whether the ground circuit is open or closed depends on the postion of the temperature selector. When set to MIN, the ground circuit should be continuously closed. Same when the OFF mode is selected. (Selecting DEFROST opens the ground circuit regardless of temp selected.)

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