Control System Logic

Climate Control System Network Communication 

The controls for the climate control system are in 1 or more locations depending on vehicle option content:

• FCIM
• FDIM (part of APIM)

When the FDIM touchscreen or voice commands are used, the APIM sends a function request message over the I-CAN to the FCIM.

When the IPC steering wheel controls are used, the IPC sends a function request message over the I-CAN to the FCIM.

The FCIM receives the climate control selections from pressing the buttons on its own controls (interface), the APIM or IPC and sends the requests to the HVAC module in the following message path:

• The FCIM sends the requests over the I-CAN to the IPC.
• The IPC then relays the requests to BCM over the HS-CAN.
• Lastly, the BCM then sends the requests to the HVAC module over the MS-CAN.

The messaging path is followed in reverse for any status updates that need to be sent from the HVAC module to the FCIM, then, if applicable, to the IPC or FDIM (through the APIM).

When an airflow mode, fresh air or RECIRC mode, temperature setting or blower speed is selected, the FCIM sends this selection to the HVAC module using the message path described above.

When A/C is selected, the FCIM sends the selection to the HVAC module using the message path described above. If the ambient temperature is sufficient, the HVAC module then sends the request to the BCM over the MS-CAN. The BCM then sends the request to the PCM over the HS-CAN.

Controls and Compressor Cycling 

The EMTC system uses inputs from the FCIM to provide the interface for the vehicle occupants to control the climate control system. When selections are made, the FCIM communicates the selections to the HVAC module, which adjusts the climate control system components to achieve the desired state. When the climate control system is operating in AUTO mode, the required climate control system settings are determined by the HVAC module. The HVAC module then adjusts the climate control system components to the desired state.

The HVAC module utilizes a FET protective circuit strategy for its actuator outputs. Output load (current level) is monitored for excessive current (typically short circuits) and is shut down (turns off the voltage or ground provided by the module) when a fault event is detected. For additional information on HVAC module FET protection, REFER to Climate Control - EMTC , Heating Ventilation Air Conditioning (HVAC) Module - EMTC.

The PCM monitors the discharge pressure measured by the A/C pressure transducer. The PCM interrupts A/C compressor operation in the event the A/C pressure transducer indicates high system discharge pressures. It is also used to sense low charge conditions. If the pressure is below a predetermined value for a given ambient temperature, the PCM will not allow the A/C clutch to engage.

The evaporator temperature sensor in an input to the HVAC module. The HVAC module maintains evaporator core temperature and prevents icing of the evaporator core by switching the A/C request signal off before the evaporator temperature is cold enough to freeze the condensation and by switching the A/C request signal on when the evaporator temperature rises above acceptable levels.

When battery voltage is applied to the A/C compressor clutch field coil, the clutch disc and hub assembly is drawn toward the A/C clutch pulley. The magnetic force locks the clutch plate and hub assembly and the A/C clutch pulley together as one unit, causing the compressor shaft to rotate. When battery voltage is removed from the A/C compressor clutch field coil, springs in the clutch plate and hub assembly move the clutch plate away from the A/C clutch pulley.

For more information on compressor operation, refer to component description, Externally Controlled Variable Displacement Compressor (2.0L/3.5L GTDI) or Internally Controlled Variable Displacement Compressor (3.5L and 3.7L Ti-VCT) in this article.

Air Handling 

Based on the climate control system settings the heater core and evaporator core housing directs airflow through the evaporator core and the heater core as needed, with the airflow exhausting through the appropriate outlets. Door actuators control the internal doors of the heater core and evaporator core housing to direct the airflow as selected by the climate control system settings. The air source is from outside air or recirculated passenger compartment air as determined by the air inlet mode door position.

The defrost/panel/floor mode door, temperature blend door and air inlet mode door actuators use a potentiometer to sense and communicate the door position to the HVAC module. When an airflow mode, desired driver or passenger temperature, or fresh air or recirculation mode is requested by the HVAC module the appropriate door actuator motor(s) is driven to the desired position, using the position sensed by the door actuator potentiometer to accurately position the door actuator.

The HVAC module will adjust the air inlet door depending on the humidity measured by the in-vehicle temperature and humidity sensor. If the vehicle cabin becomes too humid and recirculated air is not selected, the HVAC module will adjust the air inlet door to allow more recirculated air. When the humidity level drops, it will adjust back to fresh air. The HVAC module will also make system adjustments based on in-vehicle temperature.

The HVAC module uses the blower motor speed control to control the blower speed. For details on the Blower Motor Speed Control, refer to component description in this article.

MAX AC 

When MAX A/C is selected:

• the air inlet door closes, preventing outside air and admits only recirculated air.
• the RECIRC indicator is illuminated (RECIRC forced on).
• the mode doors direct airflow to the instrument panel registers.
• the temperature blend doors move to the full cool position. Blended air temperature is available.
• the A/C request button is illuminated.
• the A/C compressor operates if the outside temperature is above approximately 6 °C (42.8 °F).
• the blower motor is commanded to the highest speed. The blower motor speed is adjustable.

PANEL 

When PANEL is selected:

• the RECIRC request button is enabled. If the RECIRC request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
• the mode doors direct airflow to the instrument panel registers.
• blended air temperature is available. Only when A/C compressor operation has been selected by pressing the A/C request button (indicator on) can the airflow temperature be cooled below the outside air temperature.
• the A/C request button is enabled. The A/C compressor operates and the indicator illuminates if the A/C request button is selected and the outside temperature is above approximately 6 °C (42.8 °F).
• the blower motor is on.

PANEL-FLOOR 

When PANEL/FLOOR is selected:

• the RECIRC request button is enabled. If the RECIRC request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
• the mode doors direct airflow to the floor duct and the instrument panel registers. A small amount of airflow from the side window demisters and defrost duct is present.
• blended air temperature is available. Only when A/C compressor operation has been selected by pressing the A/C request button (indicator on) can the airflow temperature be cooled below the outside air temperature.
• the A/C request button is enabled. The A/C compressor operates and the indicator illuminates if the A/C request button is selected and the outside temperature is above approximately 6 °C (42.8 °F).
• the blower motor is on.

OFF 

When OFF is selected:

• the air inlet door closes, preventing outside air and allowing only recirculated air.
• the blower motor is off.

FLOOR 

When FLOOR is selected:

• the RECIRC request button is enabled. If the RECIRC request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
• the mode doors direct airflow to the floor duct. A small amount of airflow from the defroster duct and side window demisters is present.
• blended air temperature is available. Only when A/C compressor operation has been selected by pressing the A/C request button (indicator on) can the airflow temperature be cooled below the outside air temperature.
• the A/C request button is enabled. The A/C compressor operates and the indicator illuminates if the A/C request button is selected and the outside temperature is above approximately 6 °C (42.8 °F).
• the blower motor is on.

FLOOR-DEFROST 

When FLOOR/DEFROST is selected:

• the RECIRC request button is enabled. If the RECIRC request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
• the mode doors direct airflow to the floor duct, the defroster duct and the side window demisters.
• blended air temperature is available.
• the A/C request button toggles the indicator on and off. To reduce fogging, the A/C compressor operates automatically, regardless of indicator status, if the outside temperature is above approximately 6 °C (42.8 °F).
• the blower motor is on.

DEFROST 

When DEFROST is selected:

• the RECIRC request button is disabled. The air inlet door opens, allowing only outside air into the passenger compartment.
• the mode doors direct airflow to the defroster duct and side window demisters. A small amount of airflow from the floor duct is present.
• blended air temperature is available.
• the A/C request button toggles the indicator on and off. To reduce fogging, the A/C compressor operates automatically, regardless of indicator status, if the outside temperature is above approximately 6 °C (42.8 °F).
• the blower motor is on.