HVAC Controls, Automatic Three Zone
HVAC Controls, Automatic Three Zone
• The HVAC control for the automatic temperature control dual zone front HVAC system allows both the driver and the front seat passenger the ability to individually regulate air temperature for their side of the vehicle. Primary control for the rear HVAC system is also on the front HVAC control. An infrared sensor located in the overhead console detects thermal radiation emitted by the front seat occupants and their surroundings. All controls are identified by the graphic symbols.
• Illumination lamps for backlighting of the control.
• Computer logic that remembers the settings of the controls when the ignition is turned off and retains those settings after a restart. If the system is off when the ignition is turned off it will be off when the engine is restarted, etc.
• Computer logic that provides variable air recirculation under high temperature and humidity conditions. Because recirculation is generally accompanied by increased fan noise, the proportion of recirculated to outside air gradually approaches full recirculation over a broad temperature range.
1 Front HVAC control
• The front HVAC control and integral computer is located in the instrument panel.
2 Rotary temperature controls
• Three rotary temperature controls to select both of the front and the rear comfort temperatures from 15 to 29 °C (60 to 85 °F).
• Comfort temperatures for each zone are shown in the vacuum fluorescent digital display.
• If the set temperatures are 15 °C (60 °F) and is adjusted lower, the HVAC control will attempt to achieve the lowest temperature possible, but the display will show LO. If the set temperatures are 29 °C (85 °F) and is adjusted up, the HVAC control will attempt to achieve the highest temperature possible, but the display will show HIGH.
• Temperatures can be displayed in either Metric or Fahrenheit, which is selected from the overhead console.
3 Front fan speed control
• Rocker switch front fan speed control that can override the Auto mode.
• Bar graph is shown in the VF digital display to indicate the selected or determined front fan speed (depending on manual or auto mode).
4 Front window defogger
• Push button front window defogger control.
• An indicator lamp illuminates in the control when selected manually and the symbol appears in the VF digital display when selected by Auto mode.
5 Vacuum Fluorescent digital display
6 Air recirculation control
• Push button air recirculation control.
• An indicator lamp illuminates in the control when selected manually and the recirculation symbol appears in the VF digital display when the system exceeds 80 percent circulated air under auto mode due to high A/C demand.
7 Front mode control
• Rocker switch front mode control that can override the auto mode.
• The mode symbol appears in the VF digital display to indicate the current mode setting when selected manually or by auto mode.
8 A/C on/off control
• Push button A/C on/off control.
• The snowflake symbol appears in the VF digital display when the A/C system is in operation, whether under manual or auto mode.
9 Automatic mode control
• Push button automatic mode control to set the HVAC system to auto mode.
• FRONT AUTO appears in the VF digital display when the system is in auto mode.
10 Rear mode control
• Rocker switch rear mode control that can override the rear HVAC control and the auto mode.
• The mode symbol appears in the center portion of the VF display to show the current mode setting when selected manually or by auto mode.
11 Front heated seat controls
• Two push button front heated seat controls.
• Each control has an indicator lamp that illuminates when selected.
12 Rear HVAC controls lock
• Push button control that locks out the rear HVAC controls, allowing only the driver and front seat passenger control of the rear HVAC system.
• An indicator lamp illuminates in the control when selected.
13 Rear HVAC system on/off control
• A push button on/off control that turns the rear HVAC system completely off.
• The center portion of the VF display is blank when the rear HVAC system is off.
14 Rear window defogger
• Push button rear window defogger on/off control.
• An indicator lamp illuminates in the control when selected.
• The indicator lamp illuminates in the control even with the HVAC system turned off.
15 Rear fan speed control
• Rocker switch rear fan speed control that can override the rear HVAC control and the auto mode.
• A bar graph is shown in the center portion of the VF digital display to indicate the selected or determined rear fan speed (depending on manual or auto mode).
16 Synchronize control
• Push button synchronize control that synchronizes the temperature of all three of the comfort zones to the driver selected temperature.
• SYNC appears in the VF digital display when the system is synchronized, whether under manual or auto mode.
17 HVAC system on/off control
• Push button on/off control which allows the HVAC system to be completely turned off.
• The display is blank when the HVAC system is off.
The front HVAC control utilizes integrated circuitry and information carried on the controller area network IHS bus to monitor many sensors and switch inputs throughout the vehicle. In response to those inputs, the internal circuitry and programming of the HVAC control allows it to control the electronic functions and features of the ATC HVAC system.
The inputs received by the HVAC control of the ATC HVAC system are as follows:
• Refrigerant pressure.
• Evaporator temperature.
• Engine coolant temperature.
• Ambient air temperature.
• Infrared temperature sensor.
• Vehicle speed.
The messages sent by the HVAC control of the ATC HVAC system are as follows:
• A/C Request.
• A/C Select.
• Rear window defogger (EBL) request.
• Heated front seat requests.
The front HVAC control is diagnosed using a scan tool.
Prior to replacing an HVAC control, check for any diagnostic trouble codes related to the HVAC systems and run the calibration procedure to verify that the concern is not a system issue.
The front HVAC control cannot be repaired and must be replaced if inoperative or damaged.