Range Rover P38
AIR CONDITIONING
17
DESCRIPTION AND OPERATION
Key to A/C control diagram
1. Ambient air temperature sensor
2. Fuse 37 (ignition power)
3. Fuse 42 (battery power)
4. BeCM
5. Fuse 43 (battery power)
6. Relay 6 (auxiliary relay 1)
7. RH blower
8. RH fresh/ recirculated air servo
9. RH temperature servo
10. Distribution servo
11. LH temperature servo
12. LH fresh/ recirculated air servo
13. Evaporator temperature sensor
14. Heater coolant temperature sensor
15. In-car temperature sensor
16. ATC ECU
17. Fuse 34 (battery power)
18. Relay 7 (auxiliary 2)
19. LH blower
The air conditioning system only operates while the
engine is running. Ignition and battery power feeds for
the ATC ECU are supplied from fuses in the engine
compartment fuse box. The BeCM supplies the ATC
ECU with auxiliary power, an engine running signal
and a road speed input.
Fresh/ Recirculated air selection
The ATC ECU supplies battery voltage to the fresh/
recirculated air servos to set the position the flaps in
the air inlet housings. To change the direction of drive,
the ATC ECU reverses the polarity of the supply.
When the system is in the automatic mode, the inlet
air source is determined by ambient air temperature
and vehicle speed. The inlet air source can be
manually latched to recirculated air using the fresh/
recirculated air switch.
Blower control
Battery voltage is supplied to the positive side of the
blower motors via the auxiliary relays. Blower speed is
controlled by regulating the voltage of blower control
signals from the ATC ECU to the negative side of the
blower motors. When the blower control signals are
equal to battery voltage, the blowers are stopped.
Reducing the voltage of the blower control signals
increases blower speed until, when the signals are
earthed, the blowers are at maximum speed.
When the system is in the automatic mode, the ATC
ECU regulates the blower control signals to run the
blowers at a speed derived from the ambient air
temperature, solar heating load, vehicle speed and
distribution setting (if manually selected). When the
blower speed is set manually, the blower control
signals are regulated by the blower switch.
For diagnostic purposes, the ATC ECU monitors the
blower motor’s positive and negative voltages via the
blower voltage feedback and blower safety inputs
respectively.
Temperature control
The ATC ECU supplies battery voltage to the
temperature servos to set the position the blend flaps
in the heater unit. To change the direction of drive, the
ATC ECU reverses the polarity of the supply. The
ATC ECU determines the required position of the
blend flaps from the ambient air temperature, the
target temperatures and the fresh/ recirculated air
selection.