E36 Heater Control Issues - Feet and Windscreen Only Blows Hot

[M M 250]

I've done quite a bit of research on this and some diagnosing but I can't find a solution.

The heater in my e36 will only blow hot air to the foot and windscreen vents no matter what the settings are. As long as I select foot or windscreen, it is hot. It blows cold from the middle vents, as well as hot when the adjuster on the middle vent is turned.

I have rebuilt a heater valve unit with new seals, needles etc and installed it, made no difference. They are definitely working as I can feel and hear the solenoids clicking. I tested the voltages at the plug and they range from 7v to around 12v depending on the temperature setting on the control unit in the car.

Today I got another control unit to see if that was the problem, also no difference.

It has the dual climate electronic control module that looks like the one in the image attached.

I recently pulled out all the AC parts from the engine side but it was doing the same thing before that so I don't think it's related at all to AC.

Does anyone had any ideas what could be causing this?

Edited December 28, 2019 by M M

[zero 1162]

Hedgehog is a common failure

[Eagle 1662]

My friends E36 is like this but once the AC is on it appears to cease or maybe blend cold air into it. I never really looked into it because he hardly drives so never tested much. Im guessing you tried running full manual vent mode with everything cold? 

Assuming the heater valves are good and the control unit is functioning properly then I wonder if its some sort of connection issue from control unit to the HVAC stepper motors, possibly causing them not to shut when selecting cold given the center vents is controlled separate    

Edit: Does the E36 have an actual IHKA module as such? I know E34\E32 did which was in the dash

Edited December 28, 2019 by Eagle

[M M 250]

21 hours ago, zero said:

Hedgehog is a common failure

From my understanding this has more to do with the fan speed. Have you had it affect the temperatures as well?

19 hours ago, Eagle said:

My friends E36 is like this but once the AC is on it appears to cease or maybe blend cold air into it. I never really looked into it because he hardly drives so never tested much. Im guessing you tried running full manual vent mode with everything cold? 

Assuming the heater valves are good and the control unit is functioning properly then I wonder if its some sort of connection issue from control unit to the HVAC stepper motors, possibly causing them not to shut when selecting cold given the center vents is controlled separate    

Edit: Does the E36 have an actual IHKA module as such? I know E34\E32 did which was in the dash

I don't believe they do have IHKA.

What do you mean full manual vent mode? I'm assuming pressing the left buttons with the up and down arrows, which I have.

Is the heater valve supposed to completely shut off hot water flow when the temperature is set to coldest? If not then there may be some flaps that are not working.

[zero 1162]

Hedgehog can effect temp and speed and can be intermittent.

[Eagle 1662]

8 hours ago, M M said:

From my understanding this has more to do with the fan speed. Have you had it affect the temperatures as well?

I don't believe they do have IHKA.

What do you mean full manual vent mode? I'm assuming pressing the left buttons with the up and down arrows, which I have.

Is the heater valve supposed to completely shut off hot water flow when the temperature is set to coldest? If not then there may be some flaps that are not working.

Yeah sorry i didnt read it properly and was getting mixed up with something else. Yeah i believe valves should stop all heat regardless, not to sure if the those flaps close when cold is selected but its probably more for recirculation mode thinking about it.  

Did you manually power the valves on the bench to visually see they were sealing properly?  Maybe pull the connector and energize them with 12V directly on the car to see if that shuts the heat off. 

Haven't heard of the resistor affecting temp, not saying its impossible but you are presumable getting the correct voltage to control the valves.

[C-130 Hercules 571]

Valve shuts completely when on coldest setting. Double check valve. The only other item I can think of would be the temp dial itself. But you swapped that already. Temp sensor is unlikely faulty but pays to check as well. 

[M M 250]

9 hours ago, Eagle said:

Did you manually power the valves on the bench to visually see they were sealing properly?

No I didn't.

To be fair they were second hand as well, so they could be faulty. I'll test them and see.

Thanks guys.