Rear Window Defogger Description and Operation
Rear Window Defogger System Components
The rear window defogger system consists of the following
components:
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Rear Window Defogger
Relay |
Rear Window Defogger Operation
The rear defog control system utilizes a single zone backlight
design, driven with a single relay configuration. Additionally, up
to two outside rear view mirrors can be heated if required. A
switch for the customer to control the system is provided within
the HVAC control head. Also included in the HVAC control head is an
indicator to inform the customer with the current state of the
system. The system is only operational when engine is running or
during remote start.
Pressing the heated rear window switch on the HVAC control face
plate causes the HVAC control head to send a serial data message to
the HVAC control module requesting rear window defog operation. The
HVAC control module upon receipt of the serial data message will
provide voltage to the coil side of the rear window defogger relay,
this will energize the relay causing the relay switch contacts to
close allowing current to flow through the rear defogger grid
control circuit to the rear defogger grid.
When the rear heated window switch is pressed and the engine is
running, the rear defog control system will remain active for 10
minutes. After the initial cycle has lapsed, pressing the switch
again will continue rear window defogger operation, but the cycle
will only last 5 minutes. The rear defog control system will
function continuously if the vehicle speed is greater than 70
kilometers per hour (45 mph).
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