Air distribution control (Air conditioning)

Air distribution control

To control the air distribution within the cabin the ATC ECU signals the servo motor controlling the distribution flaps in the heater assembly to move to the flaps to the appropriate position.

In the automatic and economy modes, if the LH or RH temperature selections are set to LO or HI, air distribution is fixed as follows: l If one is set to LO and one is set to a specific temperature, to face level only. l If one is set to HI and one is set to a specific temperature, to footwells only. l If one is set to LO and one is set to HI, to face level and footwells.

When specific LH and RH temperature selections are set, air distribution is determined from the target air outlet temperatures. For higher target air outlet temperatures, air distribution is set to footwells only. For lower target air outlet temperatures, air distribution is set to face level only. For intermediate target air outlet temperatures, air distribution is set to face level and footwells. When the air distribution is set to face level and footwells, the ATC ECU varies the bias between the footwells and the face level outlets, in three stages, to provide a gradual transition of air distribution from footwells only to face level only. The three stages of bias are also employed when the air distribution is manually selected to face level and footwells.

During warm-up, the air distribution changes to face level and footwells for a period, then reverts to footwells only. The period of air distribution at face level and footwells can be cancelled by pressing and holding the on/off and defrost mode switches, then turning the ignition switch from off to on. Pressing and holding the AUTO and defrost switches, then turning the ignition switch from off to on, restores the period of air distribution at face level and footwells.

Compressor control

To engage the compressor clutch, the ATC ECU outputs a compressor clutch request to the ECM, which then energises the A/C compressor clutch relay. Compressor operation is governed by the evaporator outlet air temperature, at one of two settings, dependent on the amount of cooling required. When more cooling is required, the compressor clutch request is output if evaporator outlet air temperature increases to 4 °C (39 °F) and cancelled when it decreases to 3 °C (37 °F). When less cooling is required, the compressor clutch request is output if evaporator outlet air temperature increases to 11 °C (52 °F) and cancelled when it decreases to 10 °C (50 °F).

Engine cooling fan control

While the A/C system is on, operation of the electric engine cooling fan, to assist refrigerant condenser operation, is determined by a combination of vehicle speed and external air temperature. When cooling fan operation is required, the ATC ECU outputs a cooling fan request to the ECM, which then energises the cooling fan relay. The cooling fan request is output if vehicle speed is 80 km/h or less while the external air temperature is 28 °C (82 °F) or more. The request is cancelled, and the cooling fan switched off, if either the vehicle speed increases to 100 km/h, or the external air temperature decreases to 25 °C (77 °F).

Default settings

If the battery power supply to the ATC ECU is disrupted for any reason, e.g. battery disconnected, the system reverts to default settings when the battery power supply is restored. Default settings are: l Temperature indications in °C (in some markets a conversion connector is fitted to the ATC ECU to change the default temperature scale to °F). l LH and RH outlet temperatures of 22 °C (72 °F). l audible warning switched on. l Warm-up air distribution (to face level and footwells) function switched on. l If the system is first switched on using the A/C on/off switch, the automatic mode is engaged, regardless of the settings in use when the battery was disconnected.