System Operation: Notes

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 1990 Mercury Sable, 1990 Mercury Grand Marquis, 1990 Lincoln Town Car, 1990 Lincoln Continental, and 1990 Ford Taurus. However, it is still accessible from the selected car via links, so may be relevant.

The heated windshield will operate only under the following conditions:

Temperature of passenger compartment less than 50°F (10°C).
Engine running to give alternator output.
Battery voltage at least 11 volts.

The heated windshield is turned on by an on/off switch. When this switch is turned to ON position, a timer relay starts a 4-minute timing cycle. Power is then applied to heated windshield control module.

When the control module receives a power signal from the on/off switch (or rear defrost control switch), the control module will perform 4 functions:

Turns on driver indicator light.
Turns voltage regulator off.
Energizes alternator output control relay, switching alternator output from vehicle's electrical system to the windshield circuit.
Restores alternator's output by turning voltage regulator back on.

NOTE: When heated windshield is operating, vehicle's electrical system runs off the battery.

Battery voltage drops to 12 volts when disconnected from alternator. The voltage regulator will full field the alternator when it senses drop in battery voltage. Alternator output voltage will then rise to 30-70 volts depending on engine speed. The control module and voltage regulator limits windshield voltage to 70 volts.

If battery voltage drops below 11 volts, control module will cut off power to alternator output control relay. This action will reconnect alternator to vehicle's electrical system. After 4-minute timing cycle is over, heated windshield is turned off and charging system is returned to normal operation.