BMW E46 - Key System Functions

34
E46 Climate Control
Air Conditioning control
The air conditioning system is switched on by pressing the snow flake button and having
the blower dial on position 1 or greater. The LED in the button signals that the A/C is in
stand-by.
The IHKR control module sends the following signals to the DME over the K-bus-Kombi-
CAN -bus connection:
• IHKR on stand-by (signal AC)
• Request for A/C activation (signal KO)
• Calculated compressor load
• Request for auxiliary fan
The IHKR determines the load torque for compressor activation and required auxiliary fan
speed from the pressure sensor mounted on the high side line next to the receiver dryer.
The refrigerant pressure sensor provides a voltage input signal (0-5 volts) to the IHKR. The
voltage value increases as pressure in the high side refrigerant circuit increases. The IHKR
processes this signal to determine the calculated load that will be placed on the engine
when the compressor is switched on. Pressure values that are too high or too low will
cause the compressor to be switched off.
Once all of the criteria for compressor operation have been met, the DME control module
will activate the compressor relay to energize the compressor magnetic clutch.
Control of the evaporator temperature is carried out by the IHKR signalling the DME to shut
off the compressor when the evaporator reaches the freezing point.
0
1
2
3
4
UNLEADED GASOLINE ONLY
0
12
20
km/h
MPH
1/min
x1000
40
60
80
100
120
140
160
180
200
220
240
1
0
2
3
4
5
6
7
50
30
20
15
12
20
40
60
80
100
120
140
11
miles
BRAKE ABS
SERVICE
ENGINE
SOON
EML
!
D
M
E
K-Bus: Signal AC/KO
Evaporator Temp.
Refrigerant
Pressure
CAN-Bus
IHKR
KOMBI
M
OUTPUT
STAGE
Compressor
K19 relay
KL30
Auxiliary
Fan
The IHKR cycles the compressor
at 1
o
C if the outside temperature
is above 68
o
F. The compressor
is cycled at 3
o
C if the outside
temperature is below 68
o
F.