Operation

OPERATION

The front blower motor relay is an electromechanical switch that uses a low current input from the integrated power module (IPM) to control the high current output to the blower motor resistor (manual temperature control) or the blower motor power module (automatic temperature control). 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 blower motor.

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 blower motor relay terminals are connected to the vehicle electrical system through a receptacle in the IPM. The inputs and outputs of the blower motor relay include:

- The common feed terminal (30) receives battery current through a B(+) circuit at all times.
- The coil battery terminal (85) receives battery current through a B(+) circuit at all times.
- The coil ground terminal (86) receives a ground input through the front/rear blower motor relay control circuit only when the IPM electronically pulls the control circuit to ground.
- The normally open terminal (87) provides a battery current output to the blower motor resistor (manual temperature control) or blower motor power module (automatic temperature control) through a fuse in the IPM only when the blower motor relay coil is energized.
- The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the blower motor relay coil is de-energized.

The blower motor relay cannot be repaired and must be replaced if found inoperative or damaged. Refer to Diagrams/Electrical information for diagnosis and testing of the ISO-standard relay and for complete HVAC wiring diagrams.