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Joined: Oct 09 2019
Posts: 7

Hi...still getting to grips with my P38 and on a long drive recently I discovered something else...when I press the buttons on the hevac controller, say to change the flow of air from feet to face nothing happens. By that I mean there is no noise of the flaps moving to change air flow...is this likely to be the unit itself or something else..it has the book symbol on the screen too ...

Any suggestions please...oh...the fans seem to work as air does come out just seems to be in a fixed position. Thanks Dave

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Joined: Dec 29 2015
Posts: 743

The servos have a pot in them that develops dead bits, and the motors wear out. They use the same servos and more or less the same heater box as the Citroën XM! On those I found that I could clean up the motors a bit and get a bit more life out of them particularly if I avoided running the blower full chat when moving the flaps, because the motor controller senses an increase in current and uses that to decide when the flap is at the end of its travel. It'll run the motor each way until it stalls to get an idea where the end points are. If it can't move the flap easily because it's sticky or because the airflow is pushing back on it and the motor is a bit worn and drawing more current anyway, it'll decide that the end point is actually right in the middle of travel, or all its movement is up one end. You can try resetting it with nanocom or whatever and see if that gets it sorted.

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Joined: Dec 30 2015
Posts: 4594

Book symbol means it has detected a fault when first powered up. Do you hear the blend motors moving when you first switch on the ignition? If all 3 move from one end of their travel to the other, then there isn't a fault so they will work as they should. If a fault is detected the book symbol is bought on and the HEVAC won't try to move that blend motor. Can you adjust the temperature? If you can then the two heat blend motors are working and being driven but the distribution motor is being inhibited. You need diagnostics to confirm but I would suspect the distribution blend motor has a dead spot on the feedback pot as Gordon has outlined.

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Joined: Apr 23 2019
Posts: 508

When I was dash-off and had an issue with the RH blend motor the HEVAC unit did not move the distribution motor either in response to any of the buttons - but it would move the distribution flaps during the start-up test. Once the RH blend issue was resolved, the distribution function worked fine. Message is - don't panic - but as above, diagnostics is the key.