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93 940t no heat, electronic servo question 900

posted by  ohsotired on  Tue Dec 29 10:25 CST 2009
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last visit: Tue May 31 00:15 CST 2011
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For whatever reason, the servo that opens the door to the heater core is not functioning on my car. I replaced it, and it still does not work. It is not controlled by vacuum. It has a connection with four wires coming off it.

Are there any relays that control this, or is it 4 wires straight off the climate control unit? I swapped out the ccu with a spare, and it did not help. When i had the servo off, I manually opened the door, and I got plenty of heat.








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    93 940t no heat, electronic servo question 900

    posted by  david hunter on  Tue Dec 29 17:18 CST 2009
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    last visit: Mon Jun 30 22:10 CST 2014
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    I am not familiar with the 940 heat/AC control system but I do know a bit about the ECC system on the 960 series. Not sure what years had this but for sure the 97 did and most likely earlier years. The mixer servo is directly controlled by the electronic unit in the dash (ECC). The servo assembly on the 960 includes a pot for position feedback, I believe that whole assembly is connected by 5 wires.

    There also is a temp sensor in the dome light assembly that uses vacume to draw a small flow of cabin air over the actual sensor, I have heard of the small air entry tube or hole getting clogged with dust. The signal is used by the ECC to regulate cabin heat by open/closing the mixer shutter as needed.

    The 960 system has self diagnostics and fault codes which read from flashing of the AC OFF button light.

    I do not know if the systems are similar, the same or vastly different.
    --
    David Hunter







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