Window Defogger System Test

Electrically heated rear window defogger operation can be checked in the vehicle in the following manner:

1. Turn the ignition switch to the ON position.

Rear Window Defogger - Typical:

2. Connect an ammeter in series with the battery. Push the rear window defogger switch to the ON position. A distinct increase in amperage draw should be noted.
3. The rear window defogger operation can be checked by feeling the glass. A distinct difference in temperature between the grid lines and adjacent clear glass can be detected in three to four minutes of operation.




4. Using a DC voltmeter, connect the negative lead to Point B, and the positive lead to Point A. The voltmeter should read 10-14 volts.
5. Step 2, Step 3 or Step 4 above will confirm system operation. Indicator light illumination means that there is power available at the switch output, and does not necessarily verify system operation.
6. If turning the switch ON produced no distinct current draw on the ammeter the problem should be isolated in the following manner:
a. Confirm the ignition switch is ON.
b. Ensure that the heated rear glass feed wire is connected to the terminal or pigtail and that the ground wire is in fact grounded.
c. Ensure that the cartridge fuse and control circuit fuse are OK and all electrical connections are secure.
7. When the above steps have been completed and the system is still inoperative, one or more of the following is defective:
a. Rear Window Defogger Switch.
b. All rear window grid lines would have to be broken or one of the feed wires are not connected for the system to be inoperative.
8. If turning the switch ON produces severe voltmeter deflection, the circuit should be closely checked for a shorting condition.
9. If the system operation has been verified but indicator lamp does not light, replace the switch.