Principles Of Operation

Climate Control System

Principles of Operation

Climate Control System Network Communication

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

- Front Controls Interface Module (FCIM)

- Instrument Panel Cluster (IPC) (if equipped with steering wheel controls, Dual Automatic Temperature Control (DATC) only)

- Front Display Interface Module (FDIM) (if equipped with touchscreen controls, DATC (Dual Automatic Temperature Control) only)

For DATC (Dual Automatic Temperature Control) systems equipped with touchscreen or steering wheel controls, when the FDIM (Front Display Interface Module) touchscreen or IPC (Instrument Panel Cluster) steering wheel controls are used, they send a function request message over the Infotainment Controller Area Network (I-CAN) to the FCIM (Front Controls Interface Module).

The FCIM (Front Controls Interface Module) reads the climate control selections and sends the requests to the HVAC module in the following message path:

- The FCIM (Front Controls Interface Module) sends the requests over the I-CAN (Infotainment Controller Area Network) to the IPC (Instrument Panel Cluster) module.

- The IPC (Instrument Panel Cluster) module then relays the requests to Body Control Module (BCM) over the High Speed Controller Area Network (HS-CAN).

- Lastly, the BCM (Body Control Module) then sends the requests to the HVAC module over the Medium Speed Controller Area Network (MS-CAN).

For Electronic Manual Temperature Control (EMTC) systems, the messaging path is followed in reverse for any status updates that need to be sent from the HVAC module to the FCIM (Front Controls Interface Module) and Front Control/Display Interface Module (FCDIM).

For DATC (Dual Automatic Temperature Control) systems, the messaging path is followed in reverse for any status updates that need to be sent from the HVAC module to the FCIM (Front Controls Interface Module), FCDIM (Front Control/Display Interface Module) (non-touchscreen), FDIM (Front Display Interface Module) (touchscreen) and IPC (Instrument Panel Cluster) message center.

Climate Control System Logic

Blower Motor Speed

When blower speed is selected, the FCIM (Front Controls Interface Module) sends the desired blower speed to the HVAC module using the message path described above. The HVAC module then commands the blower motor speed control to the desired speed. The HVAC module monitors the blower motor speed control feedback circuit to make sure the blower motor is at the desired speed.

Airflow Mode Selection

When an airflow mode is selected, the FCIM (Front Controls Interface Module) determines the applicable and allowable airflow direction. The FCIM (Front Controls Interface Module) then sends this desired airflow direction to the HVAC module using the message path described above. The HVAC module determines the actuator position that is required to deliver the correct airflow direction. While monitoring the defrost/panel/floor feedback circuit, the HVAC module drives the actuator until the feedback circuit indicates the actuator has reached its required position.

Temperature Selection

When a temperature is selected, the FCIM (Front Controls Interface Module) sends the desired temperature selection to the HVAC module using the message path described above. The HVAC module then determines the temperature blend door desired position. While monitoring the temperature blend door feedback circuit, the HVAC module drives the actuator until the feedback circuit indicates the actuator has reached its desired position.

Air Inlet Selection

When fresh air or RECIRC mode is selected, the FCIM (Front Controls Interface Module) sends the desired selection to the HVAC module using the message path described above. The HVAC module drives the air inlet mode door actuator until the HVAC module detects the actuator reached its end of travel. A spike in current draw tells the HVAC module the actuator has reached the end of its travel.

A/C Selection

When A/C is selected, the FCIM (Front Controls Interface Module) 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 (Body Control Module) over the MS-CAN (Medium Speed Controller Area Network). The BCM (Body Control Module) then sends the request to the PCM over the HS-CAN (High Speed Controller Area Network).

Field-Effect Transistor (FET) Protection

A Field-Effect Transistor (FET) is a type of transistor that, when used with module software, monitors and controls current flow on module outputs. The FET (Field-Effect Transistor) protection strategy prevents module damage in the event of excessive current flow.

The HVAC module utilizes an FET (Field-Effect Transistor) 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. A short circuit DTC is stored at the fault event and a cumulative counter is started.

When the demand for the output is no longer present, the module resets the FET (Field-Effect Transistor) circuit protection to allow the circuit to function. The next time the driver requests a circuit to activate that has been shut down by a previous short (FET (Field-Effect Transistor) protection) and the circuit is still shorted, the FET (Field-Effect Transistor) protection shuts off the circuit again and the cumulative counter advances.

When the excessive circuit load occurs often enough, the module shuts down the output until a repair procedure is carried out. The FET (Field-Effect Transistor) protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the FET (Field-Effect Transistor) and the ability of the FET (Field-Effect Transistor) to withstand it. A module lifetime level of fault events is established based upon the durability of the FET (Field-Effect Transistor). If the total tolerance level is determined to be 600 fault events, the 3 predefined levels would be 200, 400 and 600 fault events.

When each tolerance level is reached, the short circuit DTC that was stored on the first failure cannot be cleared by a command to clear the DTCs. The module does not allow the DTC to be cleared or the circuit to be restored to normal operation until a successful self-test proves the fault has been repaired. After the self-test has successfully completed (no on-demand DTCs present), DTC U1000:00 and the associated DTC (the DTC related to the shorted circuit) automatically clears and the circuit function returns.

When each level is reached, the DTC associated with the short circuit sets along with DTC U1000:00. These DTCs can be cleared using the module self-test, then the Clear DTC operation on the scan tool. The module never resets the fault event counter to zero and continues to advance the fault event counter as short circuit fault events occur.

If the number of short circuit fault events reach the third level, then DTCs U1000:00 and U3000:49 set along with the associated short circuit DTC. DTC U3000:49 cannot be cleared and a new module must be installed after the repair.

The Refrigerant Cycle

During stabilized conditions (A/C system shutdown), the refrigerant pressures are equal throughout the system. When the A/C compressor is in operation, it increases pressure on the refrigerant vapor, raising its temperature. The high-pressure and high-temperature vapor is then released into the top of the A/C condenser core.

The A/C condenser, being close to ambient temperature, causes the refrigerant vapor to condense into a liquid when heat is removed from the refrigerant by ambient air passing over the fins and tubing. The now liquid refrigerant, still at high pressure, exits from the bottom of the A/C condenser and enters the inlet side of the A/C receiver/drier. The receiver/drier is designed to remove moisture from the refrigerant.

The outlet of the receiver/drier is connected to the Thermostatic Expansion Valve (TXV). The TXV (Thermostatic Expansion Valve) provides the orifice which is the restriction in the refrigerant system and separates the high and low pressure sides of the A/C system. As the liquid refrigerant passes across this restriction, its pressure and boiling point are reduced.

The liquid refrigerant is now at its lowest pressure and temperature. As it passes through the A/C evaporator, it absorbs heat from the airflow passing over the plate/fin sections of the A/C evaporator. This addition of heat causes the refrigerant to boil (convert to gas). The now cooler air can no longer support the same humidity level of the warmer air and this excess moisture condenses on the exterior of the evaporator coils and fins and drains outside the vehicle.

The refrigerant cycle is now repeated with the A/C compressor again increasing the pressure and temperature of the refrigerant.

A thermistor, which monitors the temperature of the air that has passed through the evaporator core, controls A/C clutch cycling. If the temperature of the evaporator core discharge air is low enough to cause the condensed water vapor to freeze, the A/C clutch is disengaged by the vehicle PCM.

The 2.0L Gasoline Turbocharged Direct Injection (GTDI) engine uses a Externally Controlled Variable Displacement Compressor (EVDC). The PCM pulse width modulates the solenoid in the compressor to control the compressor displacement. The PCM changes the compressor displacement based upon the:

- evaporator temperature

- ambient air temperature

- engine rpm

- vehicle speed

- A/C high side pressure

- Intake air temperature

The high-side line pressure is also monitored so that A/C compressor operation will be interrupted if the system pressure becomes too high or is determined to be too low (low charge condition).

The A/C compressor thermal protection switch interrupts compressor operation if the compressor housing exceeds temperature limits.

The A/C compressor relief valve opens and vents refrigerant to relieve unusually high system pressure.

Thermostatic Expansion Valve (TXV) Type Refrigerant System