Rear Window Heater

The automatic temperature control (ATC) module controls operation of the rear window heater using medium speed controller area network (CAN) messages to operate the rear window heater relay in the central junction box (CJB). The control module in the central junction box (CJB) interprets the controller area network (CAN) messages and switches the ground connection of the relay coil to operate the rear window heater. While the rear window heater relay is energized, a battery power feed is connected to the rear window heater elements. Rear window heater operation is only enabled when the engine is running.

The automatic temperature control (ATC) module operates the rear window heater in heating cycles of varying power and time. The heating cycle used depends on the ambient air temperature and whether it is the initial or subsequent operation during the current Power mode cycle.

When the rear window heater switch is pressed, the automatic temperature control (ATC) module illuminates an light emitting diode (LED) in the switch and initiates the appropriate heating cycle. The light emitting diode (LED) remains illuminated until the rear window heater is selected off, the heating cycle is completed or the engine stops. If the engine stalls or turned off, rear window heating resumes if the engine is re-started within 20 seconds.

On the initial selection of rear window heating, the automatic temperature control (ATC) module uses a short or long defrost phase at full power, followed by a low power phase. The defrost phase used depends on the ambient temperature. During the low power phase, the rear window heater relay is cycled off for 80 seconds and on for 40 seconds.

On subsequent operations, during the same Power mode cycle, the automatic temperature control (ATC) module operates the rear window heater at full power for a fixed time period.