Heated Windshield

Heated Windshield

The Heated Windshield System will not operate unless two conditions are met: (1) the engine must be running to provide Alternator output; and (2) the interior temperature of the vehicle must be below 50~F.

On/Off Control Switch

The Heated Windshield is activated by pressing the momentary Heated Windshield Switch ON. Power is then applied to a timer in the Heated Windshield Module.

The system is deactivated when the momentary Heated Windshield Switch is pressed OFF or when the Module timer runs out.

When the system is switched ON, the Heated Windshield Module: (1) turns on the driver indicator lamp; (2) turns the Voltage Regulator off, causing the Alternator to stop charging; (3) energizes the Alternator Output Control Relay, switching Alternator output from the vehicle's electrical system to the windshield power circuit; and (4) restores Alternator output by turning the Voltage Regulator back on.

The windshield power circuit is connected directly to the Alternator output terminal through the Alternator Output Control Relay. Operation of the remaining vehicle electrical systems depends on the Battery for power when the Heated Windshield System is operating.

Battery

After the Battery is disconnected from the Alternator, battery voltage drops to approximately 12 volts. sensing a drop in battery voltage, the Voltage Regulator full fields the Alternator.

With the Battery out of the charging circuit and with full field power, Alternator output voltage rises to between 30 and 70 volts, depending on engine speed. To prevent windshield overload at higher engine speeds, Alternator output is limited to 70 volts by the Heated Windshield Module and the electronic voltage Regulator.

If battery voltage drops below 11 volts, the Heated Windshield Module reconnects the vehicle's electrical system to the Alternator by de-energizing the Alternator Output Control Relay.

Module

The Heated Windshield Module is also connected to the EEC Module. If the system is switched on and the driver does not shift the transmission into gear, the Heated Windshield Module signals the EEC Module to increase engine speed to 1400 rpm. The higher engine idle speed ensures that the Alternator rotor is spinning fast enough to produce the required voltage. When the driver shifts the transmission into gear, the EEC Module Module resumes its normal idle speed control methods.

The Heated Windshield Module is connected to the EEC Module by the same wiring used by the A/C compressor ON signal. If the A/C is on at the same time as the Heated Windshield System, the A/C signal overrides the signal from the Heated Windshield Module.

The Windshield is of the standard three-layer construction type with a plastic laminate sandwiched between two layers of glass. Zinc oxide and silver coatings fused onto the back of the outer glass layer form the electrical conductor within the windshield.

Silver buss bars attached to the top and bottom of the windshield connect the conductive material in the glass to the power and ground circuits. The bottom buss bar is connected to the ground circuit.

Alternator Output Control Relay

When energized by the Heated Windshield Module, the Control Relay switches alternator output from the vehicle electrical system to the Heated Windshield.

Heated Windshield Module Components

In addition to its switching functions, the Heated Windshield Module has several components:

(1) a Thermistor that prevents system operation if the in-vehicle temperature is above 50~F;

(2) timers that limit system operation to four minutes per cycle;

(3) a link to the EEC Module that adjusts engine idle during certain operating conditions; and

(4) a link to the Cracked Windshield Sense Resistor that prevents system operation if the windshield is cracked.

Cracked Windshield Sense Resistor

Installation of the Cracked Windshield Sense Resistor prevents operation of the system if the windshield is cracked. The Heated Windshield Module monitors resistance across the resistor and shuts down the system if a voltage drop caused by a cracked windshield is detected.

Circuit Protection

The low voltage control circuit is protected by a 10 amp fuse located in the fuse panel. The high voltage power circuit is protected by a fusible link.