Operation

OPERATION

The ISO-standard front blower motor relay is an electromechanical switch that uses a low current input from the battery to control the high current output to the front blower motor. 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 front 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 front blower motor relay terminals are connected to the vehicle electrical system through a receptacle in the power distribution center (PDC). The inputs and outputs of the front blower motor relay include:

- The common feed terminal (30) receives battery current through a fuse in the PDC at all times.
- The coil ground terminal (85) receives a ground circuit through the integrated power module.
- The coil battery terminal (86) receives battery current through a fuse in the PDC at all times.
- The normally open terminal (87) provides battery current output to the front blower motor when equipped with the manual temperature control (MTC) system, or the blower motor power module when equipped with the automatic temperature control (ATC) system only when the front 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 front blower motor relay coil is de-energized.

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