Grand Cherokee 2WD V6-3.7L (2008)
Heated Glass Element Relay: Description and Operation
Operation
OPERATION
The rear window defogger (EBL) 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 junction block (JB) inside the vehicle. The inputs and
outputs of the EBL relay include:
-
Terminal (30) receives battery current through a fuse located in the power distribution center (PDC) at all times.
-
Terminal (85) receives a ground through the EBL relay control circuit only when the A/C-heater control electronically pulls the circuit to ground.
-
Terminal (86) receives battery current through the run relay and a fuse located in the JB only when the run relay coil is energized.
-
Terminal (87) provides battery current to the rear window defogger grid through the EBL relay output circuit and to the heated outside mirrors
through a fuse located in the JB, only when the EBL relay coil is energized.
-
Terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the EBL relay coil is
de-energized.
The EBL relay cannot be repaired and must be replaced if found inoperative or damaged. Refer to the appropriate wiring information for diagnosis and
testing of the ISO relay and for complete rear window defogger (EBL) wiring diagrams.
