IHKA Components and System

Story by Johan735
Document history
# 29 Apr 2005: Added highline comment
# 27 Jan 2004: Initial version

Introduction: The IHKA (Intergriertes Heizung und Klima Automatic) system is probably one of the systems that will cause you some major headaches over the course of your E32 ownership. The system seems really complex, but once you get a better understanding of it the system isn't that scary anymore.

I hope after reading this you have a better idea of all the parts in the system. I will not at this time discuss the working of the system or the component removal as you probably all have a Bentley manual (unlike me). As for the interior removal you can see how to get to most of the parts by looking at the "dashboard removal" and "center vents" sections of this webpage.

The climate control system of the E32 is not a completly automatic control system as it doesn't vary the fan speed on it's own. It does regulate the temperature on it's own. The system consists of a number of parts which will all be handled in the following paragraphs. The parts are:

Part list:

  • stepper motors;
  • temperature sensors;
  • air flaps;
  • the control panel;
  • the control unit;
  • the fan;
  • the fan speed controller;
  • the heater parts (heater core, water valves and aux water pump);
  • aircon specific parts (evaparator, expansion valve, compressor, condenser, aux. fan, pressure switches and the dryer).

    Parts and Locations:

    Stepper motors:

    There are ten stepper motors in the system. These are all the same motors, but two have a different connection part (mixing flaps). The motors control the flaps for:

  • 1. Passengerside footwell flap
  • 2. Passengerside dash vent flap
  • 3. Passengerside temperature mixing flap
  • 4. Driverside footwell flap
  • 5. Driverside dash vent
  • 6. Driverside temperature mixing flap
  • 7. Outside air flaps
  • 8. Recirculation mode flap
  • 9. Demister vents flap
  • 10. Rearpassengers freshair flap

  • fig 1.1 steppermotors on IHKA housing

    fig 1.2 steppermotors on IHKA housing

    fig 1.3 steppermotors on IHKA housing

    Temperature sensors:

    There are five temperature sensors in the system.

  • 1. Passengerside heatercore temperature sensor
  • 2. Driverside heatercore temperature sensor
  • 3. Controlpannel temperature sensor
  • 4. Evaporator temperature sensor
  • 5. Outside temperature sensor

  • fig 2.1 Driver/passenger temp sensor on the housing

    fig 2.2 Controlpanel temp sensor

    fig 2.3 Evaporator temp sensor on the left side of the housing

    fig 2.4 Outside temperature sensor behind bulkhead panel

    You can check the temperature sensors for proper operation by measuring their resistance. The fridge comes in handy here. And while you a near the fridge...might aswell grab a beer ;-)

    Outside Temperature Sensor
    0 Cel2.69 - 3.46 kOhm
    10 Cel1.74 - 2.11 k Ohm
    20 Cel1.15 - 1.32 kOhm
    25 Cel0.95 - 1.05 kOhm
    30 Cel0.76 - 0.87 kOhm
    40 Cel0.49 - 0.60 kOhm
    Heatercore Temperature Sensor
    -20 Cel84.39 - 109.61 kOhm
    -10 Cel48.58 - 62.09 kOhm
    0 Cel28.89 - 36.40 kOhm
    20 Cel11.13 - 13.83 kOhm
    60 Cel2.19 - 2.78 kOhm
    100 Cel0.58 - 0.77 kOhm
    Evaporator Temperature Sensor
    -5 Cel11.4 - 11.9 kOhm
    0 Cel8.8 - 9.2 kOhm
    5 Cel6.8 - 7.2 kOhm
    10 Cel5.3 - 5.6 kOhm
    15 Cel4.2 - 4.5 kOhm
    20 Cel3.3 - 3.6 kOhm
    25 Cel2.6 - 2.9 kOhm
    30 Cel2.1 - 2.3 kOhm
    35 Cel1.7 - 1.9 kOhm

    Air flaps / air ducts: There are 10 air flaps in the system. Makes sense as there are also 10 stepper motors.

  • Demister air flaps
  • Passengerside center vents flap
  • Driverside center vents flap
  • Passengerside mixing flaps
  • Driverside mixing flaps
  • Passengerside footwell airflap
  • Driverside footwell airflap
  • Rearpassenger freshair flap
  • Outside airflaps
  • Recirculation airflap
  • The system also haseight airducts:

  • left side demister duct
  • right side demister duct
  • leftside in dash vents ducs
  • rightside in dash vent duct
  • center vents ducts
  • rear passenger air ducts
  • leftside rear passenger air duct
  • rightside rear passenger air ducts

  • fig 3.1 Leftside demister airduct

    fig 3.2 Leftside in dash duct

    fig 3.3 Old style center vents ducts (pre 06/88)

    fig 3.4 New style center vents ducts (post 06/88)

    fig 3.5 New style center vents ducts fron underside

    Control panel:

    fig 4.1 Control panel without AUC

    This is one of the few parts you will all have seen :)

    Control unit: The control is mounted behind the heaterbox.

    fig 5.1 IHKA Control untit

    fig 5.2 IHKA Control unit PCB

    Blower: The fan blower is located in front of the heaterbox. It's speed is controlled by the so called sword. The sword is located inbetween the evaperator and the control unit. Erratic fan behaviour is often caused by the sword.

    fig. 6.1 "the sword"

    fig 6.2 sword PCB

    Heater specific parts:

  • Heater core
  • Heater valves
  • Aux water pump

  • fig 7.1 Heater core

    fig 7.2 Water valves and aux water pump

    Aircon specific parts:

  • Evaperator
  • Expansion valve
  • Compressor
  • Compressor relais
  • Condenser
  • Aux fan
  • Aux fan balast resistor
  • Pressure switch
  • Dryer

  • fig 8.1 Evaperator, Expansion valve, Sword and Control unit

    fig 8.2 Compressor relais located behind the driverside speaker kickpanel. Picture by Cor.
    As the 750i has two motronic systems the "compressor on" signal is send via the lock sensor control module.

    fig 8.3 Dryer with pressure switches (R12 uses 3 switches, R134a uses 1)

    If your 750iL came with a highline package you will have a second IHKA setup under the rearpart of the center console. Just to make things more complicated this box came with it's own heater core, evaporator, watervalve, control unit,...etc.

    Some pictures of the extra heater box:

    If you would like to add any comments, remarks and/or corrections to this procedure, feel free to email Mike Oswald and we'll put it on our site. Share your experiences with us so others may benefit from it.