Range Rover P38
AIR CONDITIONING
5
DESCRIPTION AND OPERATION
Evaporator and thermostatic expansion valve
High pressure liquid refrigerant is delivered to the
thermostatic expansion valve which is the controlling
device for the air conditioning system circuit. A severe
pressure drop occurs across the valve and as the
refrigerant flows through the evaporator it picks up
heat from the ambient air, boils and vaporizes. As this
change of state occurs, a large amount of latent heat
is absorbed. The evaporator is therefore cooled and
as a result heat is extracted from the air flowing
across the evaporator. The refrigerant leaves the
evaporator, on its way to the compressor, as a low
pressure gas.
Control system
The control system operates the refrigerant system
and the control flaps in the heater unit to control the
temperature and distribution of air in the vehicle
interior. It also outputs signals to the fresh/
recirculated air servos and the blowers to control the
volume and source of inlet air. The control system
consists of:
An Air Temperature Control (ATC) ECU.
An in-car temperature sensor.
An ambient air temperature sensor.
An evaporator temperature sensor.
A heater coolant temperature sensor.
A sunlight sensor.
A dual pressure switch.
A single pressure switch.
ATC ECU
The ATC ECU comprises an integrated ECU and
control panel, and is mounted in the centre console
below the in-car entertainment unit. The control panel
contains switches for system control inputs and a
Liquid Crystal Display (LCD) to provide system status
information. Inputs from the sensors and the control
panel switches are processed by the ECU, which then
outputs the appropriate control signals.
In addition to the air conditioning system, the ATC
ECU also controls the rear screen heater and, where
fitted, the windscreen heaters and the front seat
heaters. Each push switch on the control panel has a
LED to indicate the selections made.
After installation of a new ATC ECU, it must be
initialised using TestBook to ensure correct operation
of the air conditioning system.