[Scoff123]

Wondering if someone can help me out with some advice as to what might be going on with my HVAC system please?

My car is a 2011 E90 320DM Sport.
Problem = One extreme of the other temperature of air coming out of the 4 central vents when the blower is on. The thumbwheel in the centre occasionally makes some difference but not much.

Backround = A week ago I took the blower motor out in order to address the irritating squeaking sound when the blower was on low speed, which had been happening for a couple of years! While the blower was out, I also addressed the bad smell that would come from the aircon during initial startup. I used a can of Klimate Doktor foam and sprayed it in around the evaporator core, and down through all vents, following the instructions carefully. This has eliminated the bad smell, however after putting everything back together, the car developed this new problem.

I figured perhaps I knocked a connector going to one of the flap actuators, or removed it and didn't put it back, but that isn't the case. Could the dampness of the foam cleaner have caused a flap to become stuck or sticky perhaps?

Things that DO work correctly - The climate control panel appears to be working correctly and has no errors/fault codes. The 3 air distribution selection buttons of Footwell, Ventilation, and Defrost all appear to work correctly and light up when pressed. I can hear the flap motor working behind the dash when selecting each one in turn, and deselecting it again.

The windscreen clear button activates the relevant motor correctly (confirmed in ISTA).

The recirculation button activates the relevant motor correctly (confirmed in ISTA).

The 2 temperature dials adjust from 16 degrees to 28 degrees correctly, and this changes the left and right blend % and temperature or the air coming out the footwell and defrost vents correctly (confirmed in ISTA).

The Ventilation setting, although I can hear a motor running when setting this, was only producing stone cold outside air yesterday, no matter what combination of temperature settings, duct setting, or the setting of the thumbwheel in the centre. Moving the thumbwheel, I cannot hear any motor change behind the dash - so not sure if this indicates the problem?

Today however, when the car got up to temperature, only HOT air was coming from the Ventilation setting, regardless of the thumbwheel being set to cold.

Looking in ISTA, there are no errors relating to flap motors.
The front stratification flap shows some very strange numbers each time i connect and look at the readout. Sometimes the % number goes from around 90% when the thumbwheel is on cold, down to around 85% ish when its on hot, but then that number starts creeping back up towards 100% by itself without touching the thumbwheel?? Today, the figure is completely different (car hasn't moved) and remains on 8% and doesn't move regardless of me moving the thumbwheel.

Could it be that a motor is perhaps turning, but not moving the necessary flap in order to change form warm to cool air using this thumbwheel?

Initially a few days ago, the same was happening with the rear vent thumbwheel - changing from hot to cold didn't make a difference to the temp of the air coming out, however today it seemed to actually start working correctly again, and the temp changes according to the position of the thumbwheel. So something has started to work correctly again there. In ISTA, the value of the rear thumbwheel goes from 0% when on cold to 70% when hot, so very different readouts to the front problematic one.

Can anyone help please as I'm not sure what to check next, and can only think its a flap somewhere that is sticking as a result of the foam cleaner.

With the centre trim removed, should you be able to see any flaps move when the front thumbwheel is rotates from hot to cold?

[ptpending]

if you disconnected flap, you need to reinitialize the flap bus
they are sitting on one bus for control and may be lost it's addresses

[Scoff123]

Thanks, but none of the flap motors were disconnected. I have tried running the flap addressing procedure from ISTA just in case but it made no difference.

I've physically checked the motors in the passenger compartment while activating them, but I believe that the Stratification motor is up on the drivers side so will get the interior panels removed form that side and see if I can feel the motor moving when scrolling the thumbwheel. The thumbwheel readout figure does change as I rotate it, as does the resistance when measuring it on a multimeter, so I believe the potentiometer behind the thumbwheel itself is functioning correctly.
As the upstream motors appear to be working correctly, I don't believe it is a problem on the LIN bus either, so a physically stuck or sticky flap, or the Stratification motor running but not moving the flap is looking likely at the moment.

[Scoff123]

Further testing with ISTA shows the following:

I can activate the front stratification motor to 50% and to 100% and I can hear the motor working correctly.

When turning the temperature thumbwheel for the front stratification motor, there is NO activation of the motor.

This leads me to believe that the LIN bus must be OK, the Front Stratification motor must be ok, and the wiring to the motor must be ok.

The Thumbwheel varies the resistance reading across the pins as it is turned, and this also changes the reference voltage from around 0.8 to 4v from the 5v input signal, so I believe the thumbwheel potentiometer is working correctly and sending the correct reference voltage back to the IHKA.

This must mean that although the IHKA control panel is sending out the 5v signal on pin 7, and getting the varying signal back form the thumbwheel on pin 9, it is NOT activating the front Stratification motor based on this signal, so the panel must be faulty?

I have tried resetting the IHKA module, and also factory coded it just to see if it made any difference. After factory coding it, the thumbwheel actually made the front Stratification motor work temporarily for one rotation, but then it failed to respond to any further thumbwheel changes.

Unless anyone else can suggest anything else to try, does this sound like a faulty IHKA module?

[0l0dom0l0]

I've got a spare climate control panel you can have for the cost of postage if you want to try a different one.

[Scoff123]

Originally Posted by 0l0dom0l0

I've got a spare climate control panel you can have for the cost of postage if you want to try a different one.

Great, thanks for the offer - I'll send you a PM. Got to be worth a try at this stage - either that, or the Front Stratification motor works when controlled by ISTA, but is reporting the incorrect value to the IHKA control panel under normal operation. Or the IHKA is interpreting the varying voltage coming back from the thumbwheel potentiometer incorrectly.

[Scoff123]

Further tests with ISTA show some out of range values for the thumbwheel position. Should be between 0% and 100% depending on the position of the thumbwheel potentiometer, however at the 'cold' setting I am getting a 'reading' from the IHKA module of 202% and at the 'hot' setting I am getting a reading of 46%





The voltage readings were taken at both the thumbwheel connector X692, using pin 3 as -Ground, on pin 1 I have checked that I am receiving +5V out from the IHKA module from X608 (pin 7). Again on X692, I am also getting a variable voltage of between +0.8V and +4V on pin 2. This variable voltage makes it's way back to the X608 connector on the IHKA, and I read it correctly at X608 pin 9 as per the pictures above. I am using pin 5 as -Ground on X608 - this is listed as ground in the pinout table for X608.

So If I am understanding these readings, it seems the IHKA module is interpreting the varying voltage from the thumbwheel incorrectly. I would have thought that the reading of 202% from the thumbwheel in the cold position would have generated some sort of 'Implausible' reading error code. If the IHKA module is indeed faulty, then perhaps it also isn't generating a code for this out of range reading.