General

Operation
The automatic climate control system IHKR2/IHKR3 is a water-based automatic heating and air conditioning system. The control system on the water side is based on two electrically operated water valves in separate heat exchangers on the left and right sides. The required temperature in the vehicle is controlled by a mixing flap. The air is mixed ahead of the heat exchangers without being heated in the flow of ventilation air. Temperature control with mixing flaps is therefore not possible when the ventilation outlet nozzles are closed manually.

Installation Range
The IHKR2 system was installed from 01/90 thru 10/90. The IHKR3 system was installed from 11/90-on. Refer to TSB #6410913417, Nov 91.

NOTE: The IHKR3 control unit differs from the IHKR2 control unit only by the smaller control unit housing. Function and pin assignments are identical.

IHKR2/IHKR3 Control Panel:

IHKR2/IHKR3 Control Panel

Control unit
The control unit performs open-loop and closed-loop control functions with the aid of a microcomputer:
- Control of fresh air, recirculated air and mixing air flaps
- Temperature mixing
- Interior temperature control
- Rear window defogger control
- Evaporator temperature control
- Auxiliary water pump control
- Defect detection and diagnosis and making available a substitute value for failed components.

IHKR2&3 (Automatic Climate Control System) From Jan. 1990:

General Block Diagram