L322 Range Rover System Description and Operation
AIR CONDITIONING
82-50
DESCRIPTION AND OPERATION
The ATC ECU stops the FBH and de-energises the auxiliary coolant pump when any of the following occur:
l
The engine stops
l
The ambient temperature increases to more than 15
°
C (46
°
F)
l
The engine coolant temperature increases to more than 75
°
C (167
°
F)
l
The heater coolant temperature increases to more than 70
°
C (158
°
F)
l
The reference temperature decreases to less than 90%
l
The blower is selected off.
FBH Unit
Once initiated by a message from the ATC ECU, FBH operation is controlled by the ECU in the FBH unit. The ECU
controls the FBH unit at one of two heat output levels, 2.5 kW at part load combustion and 5 kW at full load
combustion.
Start Sequence: At the beginning of the start sequence the ECU energises the glow plug function of the glow plug/
flame sensor, to preheat the combustion chamber, starts the combustion air fan at slow speed and energises the
coolant circulation pump. After approximately 30 seconds, the ECU energises the FBH fuel pump at the starting
sequence speed. The fuel delivered by the FBH fuel pump evaporates in the combustion chamber, mixes with air from
the combustion air fan and is ignited by the glow plug/flame sensor. The ECU then progressively increases the speed
of the FBH fuel pump and the combustion air fan. Once combustion is established the ECU switches the glow plug/
flame sensor from the glow plug function to the flame sensing function to monitor combustion. From the beginning of
the start sequence to stable combustion takes approximately 90 seconds for a start to part load combustion and 150
seconds for a start to full load combustion.
Coolant Temperature Control: When the ECU first enters the active mode, it initiates a start to full load combustion.
Full load combustion continues until the heat exchanger casing temperature reaches 72
°
C (162
°
F), at this point the
ECU decreases the speed of the FBH fuel pump and the combustion air fan to half speed, to produce part load
combustion. The ECU maintains part load combustion while the heat exchanger casing temperature remains between
68 and 76
°
C (154 and 169
°
F). If the heat exchanger casing temperature decreases to 68
°
C (154
°
F), the ECU
switches the system to full load combustion again. If the heat exchanger casing temperature increases to 76
°
C (169
°
F), the ECU enters a control idle phase of operation.
On entering the control idle phase, the ECU immediately switches the FBH fuel pump off, to stop combustion, and
starts a timer for the combustion air fan. After a 2 minute cool down period, the ECU switches the combustion air fan
off and then remains in the control idle phase while the heat exchanger casing temperature remains above 71
°
C (160
°
F). If the heat exchanger casing temperature decreases to 71
°
C (160
°
F), within 15 minutes of the ECU entering the
control idle phase, the ECU initiates a start to part load combustion. If more than 15 minutes elapse before the heat
exchanger casing temperature decreases to 71
°
C (160 – languages can be done in-house.
°
F), the ECU initiates a
start to full load combustion.
In order to limit the build up of carbon deposits on the glow plug/flame sensor, the ECU also enters the control idle
phase if the continuous part and/or full load combustion time exceeds 72 minutes. After the cool down period, if the
heat exchanger casing is still in the temperature range that requires additional heat, the ECU initiates an immediate
restart to part or full load combustion as appropriate.
Shutdown: When the ATC ECU sends a K bus message to de-activate the FBH operation, the ECU de-energises the
FBH fuel pump to stop combustion, but continues operation of the combustion air fan and the circulation pump to cool
down the FBH unit. The cool down time depends on the combustion load at the time the message is received.
Cool Down Times
Combustion Load
Cool Down Time, Seconds
Part
100
Full
175