MG MG6 Series 2011 Service Manual page 521

HVAC-ATC
a compressor on/off request to theECM every 10 seconds. To
prevent damage to the compressor, and the formation of ice
from blocking the evaporator matrix, theBCM withholds the
change of request to compressor on, and extinguishes theLED
when the switch is released, if:
• The blower is off.
• The evaporator temperature is - 4 ℃ or below
When senses blower operation on an input taken from one of
the connections between the power controller and the blower
switch,ATCECU reads battery voltage when the blower
operates (at any speed). If the change of request is withheld
because of low evaporator temperature, theATCECU
changes the request to compressor on, when the evaporator
temperature increases to approximately 2 ℃.
When it detects the request has changed to compressor on,
theECM energises the compressor clutch relay to supply
battery power to the compressor clutch, provided the
following conditions exist:
• The pressure sensor inputs an earth to the ECM
• The evaporator temperature is above 2 ℃.
• The engine is not under hard acceleration.
• The engine coolant temperature is not too high.
• There is no engine running problem.
If one of the grant conditions no longer exists, theECM
deenergises the compressor clutch relay, to disengage the
compressor clutch, until the grant condition is restored.
If hard acceleration causes the compressor clutch to be
disengaged, after three occurrences in a single ignition cycle
theECM disregards further hard acceleration occurrences
and the compressor clutch remains engaged.
After receiving a compressor on request, theECM outputs a
compressor clutch status message to theATCECU to advise if
the request was granted or not. If the compressor on request
was granted, theATCECU keeps the A/C icon illuminated. If
the compressor on request was refused, theATCECU repeats
the compressor on request until it is granted or cancelled by:
• Pressing the A/C switch again, which changes the request
back to compressor off.
• Selecting the blower off, which changes the request back
to compressor off.
• Removing the handset.
When a compressor on request is withheld by theATCECU
or refused by the ECM, the ECON icon in theLCD is
illuminated until the request is granted or cancelled. When
the compressor is engaged:
• TheAUTO icon is illuminated if inlet air, blower speed
and distribution are all in automatic mode.
Version 2.0
• The icon on the display is illuminated provided the LH
and RH temperature are not set to LO or HI.
Once the compressor on request is granted, the compressor
remains on until the request is cancelled or the engine stops,
even if one of the grant conditions no longer exists.
If a compressor on request fails, A/C icon flashes to indicate a
fault and, on the display, theAUTO icon extinguishes and the
ECON icon illuminates.
Engine Cooling Fan Control
The ECM operates a cooling fan module to control the engine
cooling fan at one of two speeds: low and high. When the
ignition is switched on, theECM energises the main relay in
the engine compartment fuse box to supply battery power, via
fuse 4, to the cooling fan relay unit. In the cooling fan relay unit,
the battery power supply is regulated and fed to the cooling fan
motor. TheECM switches two relays in the cooling fan relay
unit to control the feed.
In addition to the refrigerant system, the cooling fan is used to
cool the engine coolant and, where applicable, the automatic
transmission fluid. When there is a conflict of the fan speed
required by the different systems, the higher speed is selected.
When a compressor on request is granted, theECM will
depend on the A/C pressure sensor output signal to control
the cooling fan relay module, and operate the fans at low or
high speed to ensure adequate cooling of the condenser.
Air Temperature Control
To determine the amount of heat or cooling required in
the passenger compartment, theATCECU uses the sensor
inputs and the temperatures selected on the control panel to
calculate target air outlet temperatures for the driver's and the
front passenger's side of the heater assembly. TheATCECU
then signals the servo motors controlling the respective
blend flaps in the heater assembly to move the flaps to the
appropriate position. The target temperatures are constantly
updated and, in the automatic mode, also used in further
calculations to determine the blower speed and the air
distribution.
The average temperature in the passenger compartment is
adapted according to the ambient air temperature. If the
ambient air temperature is very low, it increases the average
in car temperature. If the ambient air temperature is very
high, the average in car temperature is also slightly increased.
The signal provided by the solar sensor acts as a compensation
to the control algorithm to achieve a comfortable temperature
in the passenger compartment despite the solar loading. The
compensation is only effective when the air distribution is set
to the face or face/feet level positions, as passengers feel the
benefit of the compensation most at these positions.
HVAC System
505