5 Series - E34 (518i, 520i, 525td, 525tds, incl. touring) Schematics Model year 1994
Automatic climate control with filter (IHKR/F3)
Scheme 6450.5
A=X18155 26-pin, white
B=X18156 26-pin, black
C=X18157 26-pin, blue

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Pin Assignment X18155 white plug
Pin Type Description/Function Connection
1 not used
2 E Right heat exchanger temperature Right heat exchanger sensor
3 E Left heat exchanger temperature Left heat exchanger sensor
4 E Outside temperature Outside temperature sensor
5 E Evaporator temperature Evaporator sensor
6 E Setpoint, mixing air actuator Mixing air actuator
7 E Signal, independent ventilation Relay box, independent heating/ventilation
8 E Speedometer A signal Instrument cluster
9 not used
10 E Signal, independent heating Relay box, independent heating/ventilation
11 not used
12 E Terminal 58K Light switch/lights
13 A Supply voltage for function lights IHKR/F3 push button unit
14 A Supply voltage for mixing air actuator Mixing air actuator
15 M Ground for regulator in operating unit IHKR/F3 operating unit
16 M Ground for all sensors All temperature sensors
17 M Ground Mixing air actuator
18 E Push button unit lights IHKR/F3 push button unit
19 not used
20 E Signal, air condition ON IHKR/F3 push button unit
21 E Signal, recirculated air/AUC ON IHKR/F3 push button unit
22 E Signal, rear window defogger ON IHKR/F3 push button unit
23 E Function indicator, air conditioning ON IHKR/F3 push button unit
24 E Function indicator, rear window defogger ON IHKR/F3 push button unit
25 E Function indicator, AUC ON IHKR/F3 push button unit
26 E Function indicator, recirculated air ON IHKR/F3 push button unit
E = Input, A = Output, M = Ground

Pin Assignment X18156 black plug
Pin Type Description/Function Connection
1 M Ground Ground connection
2 not used
3 E Interior temperature Interior temperature sensor in IHKR/F3 operating unit
4 E Setpoint, fresh air IHKR/F3 operating unit
5 E Setpoint, left blower IHKR/F3 operating unit
6 E Setpoint, right blower IHKR/F3 operating unit
7 not used
8 E Signal AUC ON AUC control unit
9 A Signal, air conditioning ON Diode module
10 M Ground Ground connection
11 not used
12 E Terminal 30 Fuse
13 E Terminal 30 Fuse
14 not used
15 E max. heating, right IHKR/F3 operating unit
16 not used
17 not used
18 E Signal Relay box, independent heating/ventilation
19 not used
20 not used
21 not used
22 E max. heating, left IHKR/F3 operating unit
23 E Terminal 15 Fuse
24 not used
25 E Terminal 61 Unloader relay
26 E Terminal 30 h Generator
E = Input, A = Output, M = Ground

Pin Assignment X18157 blue plug
Pin Type Description/Function Connection
1 A Voltage supply for actuators all actuator motors
2 A Voltage supply for actuators all actuator motors
3 not used
4 not used
5 not used
6 A Signal, recirculated air Recirculated air flap motor
7 A Signal, recirculated air Recirculated air flap motor
8 A Signal, recirculated air Recirculated air flap motor
9 A Signal, recirculated air Recirculated air flap motor
10 A Signal, fresh air Fresh air flap motor
11 A Signal, fresh air Fresh air flap motor
12 A Signal, fresh air Fresh air flap motor
13 A Signal, fresh air Fresh air flap motor
14 A Voltage supply for potentiometer IHKR/F3 operating unit
15 A RxD diagnosis line Diagnostic connector
16 E/A TxD diagnosis line Diagnostic connector
17 not used
18 A Signal, interior sensor blower Interior sensor blower motor
19 A Signal, auxiliary water pump Auxiliary water pump relay
20 A Signal, rear window defogger ON Rear window defogger relay
21 not used
22 A Signal, A/C compressor ON Pressure switch B8y
23 A Signal, air mixing Mixing air flap motor
24 A Signal, air mixing Mixing air flap motor
25 A Signal, air mixing Mixing air flap motor
26 A Signal, air mixing Mixing air flap motor
E = Input, A = Output, M = Ground