Front Heated Windshield System

CIRCUIT OPERATION

The Heated Windshield System quickly clears ice from the windshield even in severe weather. The windshield contains a transparent resistive coating. The coating heats when power is applied to it.

Power for the system comes directly from the generator. The engine must be running for the system to operate.

Components
The system consists of the special windshield, Heated Windshield Power Module, Heated Windshield Control Module, Heated Windshield Switch, and a special generator. The Transaxle Range Switch is used as an input to the system.

The Heated Windshield Control Module receives various inputs. Using electronic logic it determines when the system should turn on.

The Generator is a special model. Three phase AC voltage from the stator is brought out to a connector on the back of the unit. The Generator can continue to supply its normal DC output while AC power is being supplied. While the windshield does not draw current from the battery it does reduce the charging current available to the battery.

The Heated Windshield Power Module receives AC power from the generator, steps up the voltage to approximately 60 volts in the transformer, rectifies it to DC, and supplies it to the windshield. This module also contains a relay which switches its output on and off. The relay is controlled by the Heated Windshield Control Module.

The PCM increases idle speed when the vehicle is in park or neutral and the system is operated.

Operation
When the car's engine is running, the heated windshield system may be turned on by pressing the Heated Windshield Switch. The switch momentarily grounds terminal A3 of the Heated Windshield Control Module. This signals the control module to begin the turn-on sequence and to turn on the switch LED.

The module Starts the turn-on sequence by checking that more than 11.2 volts is present at terminal B6. This ensures that adequate voltage is available for the other circuits.

The control module also checks that the windshield is not cracked. This is sensed at control module terminals A2 and B4.

Once the previous conditions are met, the control module determines if the transaxle is in park or neutral by monitoring the Transaxle Range Switch state at terminal B3. If the Park Neutral input at terminal B3 is grounded through the range switch, the control module signals the Powertrain Control Module (PCM) to increase the engine idle speed. The module signals the PCM by grounding the PCM's Fast Idle Request input terminal 1D12 (4.9L) or ZD7 (Northstar) at the Heated Windshield Control Module's A4 terminal.

The Heated Windshield Control Module now switches on its relay control output terminal B1. This energizes the Heated Windshield Power Module Relays. Power is now drawn from the generator, stepped up and rectified by the power module, and supplied to the windshield through CKT 365.

Timing
The control module has a timing feature similar to the rear defogger's. The first time the switch is pressed after starting the engine results in a 4 minute cycle. Pressing the switch again will result in a 2 minute cycle. If the ignition is turned off for more than 5 seconds, the timing cycle resets to 4 minutes. The system may be turned off by depressing the switch again after the system has been enabled.

If the car is shifted out of park or neutral while the system is activated within the first 2 minutes of the cycle, the first cycle will be reduced to 2 minutes. If 2 minutes have already elapsed, the system will finish the 4 minute cycle.

Crack Detection
The crack detection circuit monitors the voltage at the vertical bus (reference voltage) and at the narrower vertical sense trace (sense voltage). A crack through either or both of these will cause a voltage difference between terminals A2 and B4 of the control module. If the control module senses a difference of more than 10 volts between these terminals, it will shut the system down.