Thread: A/C and Heater Control Head problem?
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Old Oct 14, 2012 | 08:02 PM
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onehundred80
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Default Re: A/C and Heater Control Head problem?
Originally Posted by GraphiteGhost

180, I read the link, thanks for that it showed a detail I needed to know if it was proportional or on/off. I also found out why the duo-valve is hot when not calling for heat! Its failsafe open (heat mode), it requires current to close. Also, it does pulse based on a littany of inputs from all the temp sensors and the sensors in the A/C system, as well as the settings/demand from the driver/passenger.
I do not think they will pulse, the valves can be activated by the driver or passenger. One is the passenger side valve and the other the driver side valve. They should not go up and down like a yo yo. I have found threads on the Mercedes forums where they have to be lubricated as they can stick. I am no wiz on this stuff but is it not possible that if the bobbin was not fully in the attracted position that the energy trying to pull it up/down whatever would lead to overheating?

If they were pulsating then a poor connection or an intermittent signal may be the culprit.

In some circumstances the heater and the AC are running at the same time even if the AC is in the OFF position. The AC being used to dehumidify the air for the windshield on cold days.
 
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