AIR CONDITIONING (page 2 of 3)

AIR CONDITIONING

DESCRIPTION AND OPERATION

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Heater Distribution and Blend Unit Control
Blower unit air flow, having passed through the evaporator passes into the heater blend unit to be heated, if required. 
It is then directed into the vehicle interior in accordance with the flap positions, which are designated by the air 
distribution control on the fascia panel. A heater flap controls the amount of air flowing through the heater matrix, this 
flap is moved in response to temperature selection using the knob on the control panel.

The distribution control moves the flaps which control the direction of the air flow into the interior of the vehicle.

Compressor and Cooling Fan Operating Conditions
The Engine Control Module (ECM) controls the compressor and cooling fan operation in response to signals received 
from the refrigerant pressure sensor, evaporator temperature sensor and engine coolant temperature sensor, either 
directly or  on the CAN Bus from the instrument pack. The refrigerant pressure can be low, medium or high, the system 
operating characteristics applicable for each condition is shown in the following table:

* With pressure below the low pressure limit, the cooling fans will always be off unless air conditioning is running whilst 
evaporator temperature drops below minimum. If evaporator temperature drops below minimum, the cooling fans are 
required to prevent cabin temperature cycling.

The engine management system also drives fan speed based on engine temperature. A faster cooling fan request 
from either the engine cooling control or the A/C system will override another slow cooling fan speed request.

A/C Compressor On/

Off

Refrigerant Pressure Sensor 

Operating Range

Action

Off

MED range

Air Con MED limit reached, cooling fans switched to High 
speed.

Off

NORMAL range

Normal Condition, Low fan speed - no additional action

Off

HIGH range

COMPRESSOR NOT ALLOWED TO BE TURNED ON, 
cooling fans at high speed

Off

LOW range

COMPRESSOR NOT ALLOWED TO BE TURNED ON*

On

MED range

Air Con MED limit reached, cooling fans to High speed

On

NORMAL range

Standard condition, low fan speed - no additional action

On

HIGH range

AIR CON COMPRESSOR MUST BE DISENGAGED 
IMMEDIATELY, cooling fans set to High speed.

On

LOW range

AIR CON COMPRESSOR MUST BE DISENGAGED 
IMMEDIATELY*