Rear Defogger Relay - Operation

OPERATION

The ISO-standard rear window defogger (EBL) micro-relay is an electromechanical switch that uses a low current input controlled by the A/C-heater control to control the high current output to the rear window defogger grid lines. The movable, common feed relay contact is held against the fixed, normally closed relay contact by spring pressure. When the electromagnetic relay coil is energized, it draws the movable common feed relay contact away from the fixed, normally closed relay contact and, holds it against the fixed, normally open relay contact. This action allows high current to flow to the rear window defogger grid lines.

When the relay coil is de-energized, spring pressure returns the movable relay contact back against the fixed, normally closed contact point. The resistor or diode is connected in parallel with the relay coil, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The EBL relay terminals are connected to the vehicle electrical system through a receptacle in the power distribution center (PDC). The inputs and outputs of the EBL relay include:

- The common feed terminal (86) receives a battery current input from a fuse in the PDC through a fused B(+) circuit at all times.
- The coil ground terminal (83) receives a ground input from the A/C-heater control when the A/C-heater control electronically pulls the control circuit to ground.
- The coil battery terminal (85) receives a battery current input from the body control module (BCM) only when the ignition switch is in the Run position.
- The normally open terminal (82) provides a battery current output to the rear window defogger through the relay output circuit only when the rear window defogger relay coil is energized.
- The normally closed terminal (82A) is not connected to any circuit in this application, but provides a battery current output only when the rear window defogger relay coil is de-energized.

The EBL micro-relay cannot be repaired and must be replaced if inoperative or damaged. Refer to the appropriate wiring information for diagnosis and testing of the ISO-standard micro-relay and for complete rear window defogger (EBL) wiring diagrams.