Range Rover FBH System Description: Efficient Air Conditioning System Operation
AIR CONDITIONING
82-26
DESCRIPTION AND OPERATION
Heater Matrix Temperature Sensor
The heater matrix temperature sensor is a NTC thermistor that provides the ATC ECU with a temperature signal from
the air outlet side of the heater matrix. On low line systems, a single sensor is installed in the rear of the heater
assembly casing, to the right of the centre-line. On high line systems, two sensors are installed, one each side of the
centre-line.
The ATC ECU uses the input from the heater matrix temperature sensor(s) to control the operation of the coolant
valve(s).
The signal voltage from each heater matrix temperature sensor is between 0 and 5 V. The ATC ECU monitors the
signal voltage and defaults to a temperature of 55
°
C (131
°
F) if it goes out of the range 0.173 – 4.890 V:
l
If the signal voltage is less than 0.173 V, the ATC ECU assumes there is a short circuit to ground
l
If the signal voltage is more than 4.890 V, the ATC ECU assumes there is an open circuit or a short circuit to
battery.
Sunlight Sensor
The sunlight sensor consists of two photoelectric cells that provide the ATC ECU with inputs of light intensity, one as
sensed coming from the left of the vehicle and one as sensed coming from the right. The inputs are a measure of the
solar heating effect on vehicle occupants and used by the ATC ECU to adjust blower speed, temperature and
distribution to improve comfort. The sensor is installed in the centre of the fascia upper surface.
If one of the photoelectric cells is faulty, the output from the other photoelectric cell is used for both sides of the vehicle.
If both photoelectric cells are faulty, the ATC ECU uses a default value of zero.
Pollution Sensor
The pollution sensor allows the ATC ECU to monitor the ambient air for the level of hydrocarbons and oxidized gases
such as nitrous oxides, sulphur oxides and carbon monoxide. The pollution sensor is installed at the rear of the
radiator, on the upper RH side of the viscous fan housing.
The ATC ECU outputs a battery power supply to heat the pollution sensor to operating temperature, and a 5 V
reference voltage for the signal. The signal voltage from the pollution sensor is between 0 and 5 V.
If there is a fault with the pollution sensor, the ATC ECU disables automatic closing of the recirculation flaps on
detection of pollutants.
Auxiliary Coolant Pump
The auxiliary coolant pump is an electric pump that ensures there is a satisfactory flow rate through the heater matrix
at low engine speeds. The auxiliary coolant pump is installed in the engine compartment, in a rubber mounting
attached to the side of the LH suspension turret. Operation of the auxiliary coolant pump is controlled by a power
supply from the ATC ECU.
Coolant Valve
The coolant valve controls the coolant flow to the heater matrix. A single coolant valve controls the coolant flow to
both sides of the heater matrix on low line systems. On high line systems, separate coolant valves control the coolant
flow to each side of the heater matrix. The coolant valves are installed in the engine compartment on a bracket
attached to the side of the LH suspension turret.
Each coolant valve is a normally open solenoid valve controlled by a Pulse Width Modulated (PWM) signal from the
ATC ECU. The ATC ECU changes the length of time the coolant valve is open each duty cycle between 0 second
(valve closed) and 3.6 seconds (valve held open). On the high line system, the PWM signals to the two valves are
phase offset by 1.8 seconds to reduce coolant flow fluctuations.
FBH System
The system consists of a FBH unit, a FBH fuel pump and a changeover valve. On vehicles with the remote operation
feature, the system also includes a FBH receiver and a remote handset.
Fuel for the FBH system is taken from the vehicle fuel tank, through a line attached to the fuel tank's fuel pump unit,
and supplied via the FBH fuel pump to the FBH unit. In the FBH unit, the fuel delivered by the FBH fuel pump is burned
and the resultant heat output is used to heat the engine coolant. The changeover valve isolates the heater coolant
circuit from the engine coolant circuit