Front Heated Windshield System

CIRCUIT DESCRIPTION:
The Heated Windshield System provides quick clearing of ice from the windshield even under severe winter conditions. The windshield contains a transparent internal 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 to operate the system.

COMPONENTS:
The system consists of the special windshield, a Heated Windshield Power Module, a Heated Windshield Control Module, ECM, a special Generator and a Heated Windshield Switch. The PCM is used to control engine idle speed.

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 voltage while AC power is being supplied.

The Heated Windshield Power Module receives AC power from the Generator, increases the voltage in an autotransformer, 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 is used to increase idle speed in Park or Neutral during Heated Windshield operation.

The Heated Windshield System is activated by pressing the DE-ICE Switch on the HVAC Control Panel or the DE-ICE Soft Key on the VIC with the engine running.

The DE-ICE request is sent through the serial data line to the BCM. The BCM then signals the Heated Windshield Control Module to turn on the system by momentarily pulling circuit 648 to ground. The Control Module supplies the BCM with system "ON/OFF" status through circuit 649. When the system is "ON," voltage is applied through circuit 649 to the BCM. When the system is "OFF," no voltage is applied to the BCM through circuit 649. The BCM updates the HVAC Control Head or the CRTC with system "ON/OFF" status through the serial data line for the DE-ICE LED or DE-ICE Soft Key Control.

Before activating the System, the Control Module checks that more than 11.2 volts is present at terminal 136. This is to ensure that adequate battery voltage is available for the other circuits. While the windshield does not draw current from the Battery, it does reduce the charging current available to the Battery.

The Control Module also checks that the Windshield is not cracked. This is sensed at Control Module terminals A2 and 134. (See Special Feature).

If all the above conditions are met and the Transaxle is in park or neutral, the Control Module signals the PCM to increase engine idle speed by grounding Control Module terminal A4. The PCM will respond by increasing engine idle speed.

The Control Module then switches "ON" its output at terminal B1. This energizes the Heated Windshield Power Module Relays. Power is then drawn from the Generator, stepped up and rectified by the Power Module and supplied to the Windshield which heats.

TIMING CYCLES:
The Control Module incorporates a timing feature similar to the Rear Defogger. The first time the switch is pressed after starting the engine results in a 4 minute on cycle. Pressing the switch again will result in a 2 minutes cycle. If the Ignition is turned OFF for more than 5 seconds the timing cycle will reset to 4 minutes. The system may be turned OFF by depressing the switch again.

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.

SPECIAL FEATURE:
CRACK DETECTION. The crack detection circuit monitors the voltage at two points in the system. They are 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 134 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.