
Published: 11-May-2011
Climate Control System - General Information - Air Conditioning (A/C) System
Flushing
General Procedures
1. WARNINGS:
Use extreme care and observe all safety precautions related to the
use of refrigerants. Due to refrigerant hazards, always wear safety
goggles and non-penetrable gloves when working on or flushing air
conditioning (A/C) systems. Failure to follow this instruction may result
in personal injury.
When flushing the A/C system, refer to the manufacturers
equipment instructions for additional information. Failure to do so may
result in system damage or personal injury.
The A/C refrigerant analyzer must be used before the recovery of
any vehicle's A/C refrigerant. Failure to do so puts shop bulk refrigerant
at risk of contamination. If the vehicle A/C refrigerant is contaminated,
refer the customer to return to the repair facility that performed the last
A/C repair. If the customer wishes to pay the additional cost, use the
A/C recovery equipment that is designated for recovering contaminated
A/C refrigerant. All contaminated A/C refrigerant must be disposed of as
hazardous waste. For additional information, refer to the manufacturers
equipment instructions. Failure to follow this instruction may result in
personal injury.
Prior to using the A/C flushing equipment for the first time, follow
the operating instructions. Failure to follow this instruction may result in
personal injury.
CAUTION: Prior to flushing, remove and discard the desiccant sack.
Depending on the equipment used, other A/C components may have to
be removed prior to flushing. For additional information, refer to the
manufacturers equipment instructions before flushing the A/C system.
Recover the refrigerant.
For additional information, refer to Air conditioning (A/C) System Recovery, Evacuation and Charging in this section.
2. Remove the desiccant sack.
For additional information, refer to Section 412-03 Air Conditioning.
3. Flush the system. For additional information, refer to the manufacturers
equipment instructions.
4. Install new refrigerant lines if blocked with debris.
5. Install a new desiccant sack.
For additional information, refer to Section 412-03 Air Conditioning.
6. Add the required amount of oil to the A/C system depending on the
repair procedure.
For additional information, refer to Refrigerant Oil Adding in this section.
7. Evacuate and charge the A/C system.
For additional information, refer to Air conditioning (A/C) System Recovery, Evacuation and Charging in this section.
8. Carry out fluorescent dye leak detection test.

control switch on the integrated control panel or the + and - soft buttons on the touch screen display (TSD). The ATC module also adjusts blower speed to compensate for the ram effect on inlet air produced by forward movement of the vehicle. As
vehicle speed and ram effect increases, blower motor speed is reduced, and vice versa.
Air Distribution Control
Two air distribution doors are used to direct air into the passenger compartment. The doors are operated by stepper motors,
which are controlled by the ATC module using LIN bus messages.
When the A/C system is in automatic mode, the ATC module automatically controls air distribution into the passenger compartment in line with its 'comfort' algorithm. Automatic control is overridden if any of the TSD air distribution soft buttons
are selected. Air distribution in the passenger compartment will remain as selected until the 'Auto' switch is pressed or a
different manual selection is made.
A/C Compressor Control
When A/C is selected the ATC module maintains the evaporator at an operating temperature that varies with the passenger compartment cooling requirements. If the requirement for cooled air decreases, the ATC module raises the evaporator operating temperature by reducing the flow of refrigerant provided by the A/C compressor. The ATC module closely controls the rate of temperature increase to avoid introducing moisture into the passenger compartment.
If the requirement for cooled air increases, the ATC module lowers the evaporator operating temperature by increasing the flow of refrigerant provided by the A/C compressor.
When A/C is off, the compressor current signal supplied by the ATC module holds the A/C compressor solenoid valve in the minimum flow position, effectively switching off the A/C function.
The ATC module incorporates limits for the operating pressure of the refrigerant system. If the system approaches the high pressure limit, the compressor current signal is progressively reduced until the system pressure decreases. If the system falls
below the low pressure limit, the compressor current signal is held at its lowest setting so that the A/C compressor is maintained at its minimum stroke. This avoids depletion of the lubricant from the A/C compressor.
A/C Compressor Torque
The ATC module transmits refrigerant pressure and A/C compressor current values to the ECM (engine control module) over the medium speed then high speed CAN bus, using the CJB as a gateway. The ECM uses these values to calculate the torque being used to drive the A/C compressor. The ECM compares the calculated value with its allowable value and if necessary forces the ATC module to inhibit the A/C compressor by transmitting the 'ACClutchInhibit' CAN message. This forces the ATC module to reduce the drive current to the A/C compressor solenoid valve, which reduces refrigerant flow. This in turn reduces the torque required to drive the A/C compressor.
By reducing the maximum A/C compressor torque, the ECM is able to reduce the load on the engine when it needs to maintain vehicle performance or cooling system integrity.
Cooling Fan Control
The ATC module determines the amount of condenser cooling required from the refrigerant pressure sensor, since there is a direct relationship between the temperature and pressure of the refrigerant. The cooling requirement is broadcast to the ECM on the medium speed CAN bus. The ECM then controls the temperature of the condenser using the cooling fan.
Programmed Defrost
The programmed defrost DEF switch is located on the integrated control panel. When the switch is pressed, the ATC module instigates the programmed defrost function. When selected, the ATC module configures the system as follows:
Automatic mode off.
A/C on. Selected temperature unchanged.
Air inlet set to fresh air.
Air distribution set to windshield.
Blower speed set to level 6.
Windshield heater (where fitted) and rear window heater on.
The programmed defrost function can be cancelled by one of the following:
Selecting any air distribution switch on the TSD.
Pressing the AUTO switch on the integrated control panel.
A second press of the DEF button.
Switching the ignition OFF.
The blower speed can be adjusted without terminating the programmed defrost function.
Rear Window Heater
Rear window heater operation is only enabled when the engine is running. The ATC module controls operation of the rear window heater using a relay in the RJB. When rear window heater operation is required, the ATC module broadcasts a message to the RJB on the medium speed CAN bus. On receipt of the message, the RJB energizes the relay by providing a ground path for the relay coil. This allows a battery feed to flow across the relay to power the rear window heater element.

rear window heater switch is pressed or the engine stops.
Automatic operation during a journey is initiated when low ambient air temperatures are experienced and the vehicle has been
travelling for a set period of time above a threshold speed. In this instance, no feedback is given to the driver to inform him
the rear window heater is operational (the switch LED is not illuminated). The duration of heater operation is variable depending on the ambient air temperature, vehicle speed and the amount of time the vehicle has been travelling.
Windshield Heater (Where Fitted)
Windshield heater operation is only enabled when the engine is running. The ATC module controls operation of the windshield heater using two relays in the EJB (engine junction box). When windshield heater operation is required, the ATC module broadcasts a message to the CJB on the medium speed CAN bus. On receipt of the message, the CJB energizes the relays by providing a ground path for both relay coils. This allows a battery feed to flow across the relays to power the windshield left
and right heater elements.
There are two modes of windshield heater operation; manual and automatic.
Manual operation is activated by pressing the windshield heater switch on the integrated control panel. When the switch is
pressed, the status LED in the switch illuminates and the windshield heater elements are energized. Manual operation is discontinued when the windshield heater switch is pressed a second time, 5 minutes have elapsed (the heating phase), or the
engine stops. If manual operation is discontinued by the engine stopping, the previous heating phase is resumed if the engine
is re-started within 30 seconds.
There are two variants of automatic operation; automatic operation at the start of a journey and automatic operation during a
journey.
Automatic operation at the start of a journey is initiated if the ambient air temperature is below 5 °C (41 °F). In this instance,
the switch LED is illuminated and the heater elements are energized for 6.5 minutes. Automatic operation is discontinued if the windshield heater switch is pressed or the engine stops.
Automatic operation during a journey is initiated when low ambient air temperatures are experienced and the vehicle has been
travelling for a set period of time above a threshold speed. In this instance, no feedback is given to the driver to inform him
the windshield heater is operational (the switch LED is not illuminated) and the duration of operation is variable depending upon the ambient air temperature, vehicle speed and the amount of time the vehicle has been travelling.
Exterior Mirror Heaters
Operation of the exterior mirror heaters is fully automatic and not controllable by the driver. Exterior mirror heater operation is
determined by ambient air temperature and windshield wiper status. When ambient air temperature reaches a pre-determined
level, the ATC module broadcasts an exterior mirror heating request to the door modules over the medium speed CAN bus. On receipt of this message, the door modules provide feed and ground connections to both exterior mirror heater elements.
The amount of time the exterior mirror heaters are operational increases if the windshield wipers are switched on. This ensures
the mirrors remain mist free in damp and wet conditions, where there is an increased risk of misting.
Seat Heaters (Where Fitted)
There are four seat heater settings available; off, 1, 2 and 3, which can be selected on the home and climate control screens
of the TSD. The heat setting is relayed to the vehicle occupants through a graduated display on the TSD.
Operation of the heated seats is controlled by the ATC module. When the ATC module receives a heating request from the TSD, it broadcasts a message to the CJB over the medium speed CAN bus. The CJB then provides a hardwired 12 V supply to the three heater elements in the related front seat. The heater elements, two in the seat cushion and one in the seat squab,
are wired in series. The ATC module monitors seat temperature using a temperature sensor located in each seat cushion. The CJB provides the temperature sensors with a 5 V supply. The level of the returned voltage back to the CJB is proportional to the seat temperature. The value of the return signal is broadcast to the ATC module, over the medium speed CAN bus, which allows it to control the seat temperature to the required level. The ATC module will suspend or disable operation of the seat heaters if any of the following occur:
Battery voltage exceeds 16.5 ± 0.3 V for more than 5 seconds. Seat heating is re-enabled when battery voltage
decreases to 16.2 ± 0.3 V.
If a short or open circuit is detected.
If the seat heat temperature rises significantly above the target temperature setting.
The graduated display on the TSD remains illuminated until the seat heaters are turned off or the engine stops. If the engine
is restarted within 30 seconds the seat heater resumes the previous heating level.