Heat at Rear Vent
 

Hi all. Tried doing a search, but search function isn't working. I am getting hot air out of the rear seat vent at the back of the center console. Even when the fan is off and the control is set to cool. The heat also blows if the fan is on. I don't get cool air out of it even if the AC is on. Anyone have a diagram of how the ventilation system works?

Stuck or broken control flap
Those are in the heater box matrix under the dash.

What version you have: manual AC (IHKR), auto AC (IHKA), IHKA with additional rear ventilation option?

I have IHKA with rear ventilation. I almost never use the AUTO function is that would make a difference.

Doesn’t really matter. The controls in the back dictate the temp of the air coming out of the rear vents…
But again you’ll need to check if the valves are working or even if the temperature control slide is still functioning. A simple resistance measurement should take care of it.

The rear console temperature control (stratified air) thumbwheel is a simple potentiometer. That signal goes to IHKA which operates the rear stratification flap with servo motor on the main HVAC unit. (If the rear blower setting is on zero the basic setting for rear temp is always on warm as a default regardless of the rear temp wheel setting. Reducing cold draft.)

With diagnostics you can check how IHKA sees the temp setting and can activate that servo motor. Like said with simple multimeter you could check if the temp potentiometer is working.

This E39 IHKA document applies to E53 too.

https://dokumen.tips/documents/bmw-e...ng.html?page=1

Thank you! Very helpful