Temperature Mixing

IHKR1 TEMPERATURE MIXING







Temperature mixing, a feature unique to BMW climate control systems, allows the driver to change the temperature of the air discharged from the face-level outlets. This feature is also known as the "stratified air" feature.

A set of flaps is located above the area between the evaporator core and the heater cores.

Opening these flaps allows air that has passed through the evaporator core to leave the housing before passing through the heater cores. The air going to the face-level outlets can thus be cooler than air going to other outlets (footwell or defroster).

The left and right mixing flaps are operated as a pair by the mixing flaps stepper motor.

The control module uses these inputs to determine mixing flap position:
- Temperature mixing potentiometer (most important)
- Interior temperature sensor
- Left desired-temperature knob
- Microswitch on drive mechanism for face-vent flaps
- "y" factor, which is calculated by control module







The temperature mixing potentiometer is actuated by rotating the thumbwheel located between the Instrument Panel center face-vent outlets.

There is a microswitch mounted on the housing assembly at the lever for the vent flaps. The microswitch is used to override the temperature mixing potentiometer input when the middle, face-outlet slide lever is moved all the way to the left (face-vent flaps are closed).

When the control module receives the "face-vent flaps closed" signal, it positions the mixing flaps in the "warmest air" position (all air directed through the heater cores).







Prior to engine startup, the mixing flaps are in the warmest air position. When the ignition switch is turned to "Run," the mixing flaps open to a position determined by the control module. At engine shutdown, the mixing flaps again close automatically to the warmest air position.