Commander 4WD V8-4.7L VIN N (2006)
Blower Motor Relay: Description and Operation
Rear
RELAY-BLOWER MOTOR
DESCRIPTION
The blower motor relay (1) for the rear heating-A/C system is an International Standards Organization (ISO)-type relay. Relays conforming to the ISO
specifications have common physical dimensions, current capacities, terminal functions and patterns (2). The rear blower motor relay is a
electromechanical device that switches battery current through a fuse in the power distribution center (PDC) directly to the rear blower motor when
equipped with the manual temperature control (MTC) system. The rear blower motor relay is energized when the relay coil is provided battery current by
the rear A/C-heater control switch located in the dash panel.
The rear blower motor relay is located in top side of the fuse block in the passenger compartment.
OPERATION
The ISO-standard blower motor relay is an electromechanical switch that uses a low current input from the ignition switch to control the high current
output to the 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 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 power distribution center (PDC). The inputs
and outputs of the blower motor relay include:
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Terminal (30) receives fused battery current at all times.
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Terminal (85) is connected to a ground circuit at all times.
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Terminal (86) receives fused battery current through the run relay only when the run relay coil is energized.
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Terminal (87) provides fused battery current to the blower motor through the blower motor relay only when the blower motor relay coil is
energized.
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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, if faulty or damaged, it must be replaced. Refer to the appropriate wiring information for diagnosis and
testing of the ISO-standard relay and for complete HVAC wiring diagrams.
