Heating Ventilation Air Conditioning (HVAC) Control Module

The DATC climate control system uses the center display unit touch screen and climate control panel for all adjustments of climate control settings. For details on the HVAC control module communication, refer to Control System Logic in this procedure.

The HVAC control module is on the MS-CAN and sets DTCs. A/C requests are sent to the GWM and then to the PCM via the FD-CAN.

The temperature control setting for driver temperature control and passenger temperature control setting for DATC adjusts the discharge air temperature. Movement of the temperature setting from cool to warm causes a corresponding movement of the temperature door. The position of the temperature door determines the discharge air temperature.

The airflow mode setting adjusts the discharge air outlet location. Each airflow mode selector icon causes a corresponding movement of the airflow mode doors and determines the discharge air outlet location.

The A/C button determines A/C compressor operation, except when the temperature selector is set to MAX A/C or the airflow mode selector is in Defrost mode.

The recirculated air request selection can be activated in any mode except Defrost. In MAX A/C mode the recirculated air indicator is illuminated (recirculated air forced on).

The HVAC control 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. 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 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 protection) and the circuit is still shorted, the FET 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 protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the FET and the ability of the FET to withstand it. A module lifetime level of fault events is established based upon the durability of the FET. 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 Diagnostic Trouble Codes (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 that the fault has been repaired. After the self-test has successfully completed (no on-demand Diagnostic Trouble Codes (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 Diagnostic Trouble Codes (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 Diagnostic Trouble Codes (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 HVAC control module requires PMI when it is replaced.