Liberty 4WD L4-2.4L DOHC VIN 1 (2005)
Compressor Clutch Relay: Description and Operation
A/C Clutch Relay
The A/C clutch relay is a International Standards Organization (ISO) micro-relay Relays conforming to the ISO specifications have common physical
dimensions, current capacities, terminal functions and patterns. The ISO micro-relay terminal functions are the same as a conventional ISO relay.
However, the ISO micro-relay terminal pattern (or footprint) is different, the current capacity is lower, and the physical dimensions are smaller than those
of the conventional ISO relay.
The A/C clutch relay is located in the power distribution center (PDC) in the engine compartment.
The A/C clutch relay is an electromechanical switch that uses a low current input controlled by the powertrain control module (PCM) or engine control
module (ECM), depending on engine application, to control the high current output to the A/C clutch field coil. 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 A/C clutch field coil.
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 A/C clutch relay terminals are connected to the vehicle electrical system through a receptacle in the power distribution center (PDC). The inputs and
outputs of the A/C clutch relay include:
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The common feed terminal (30) receives battery current through a fuse in the PDC at all times.
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The coil ground terminal (85) receives a ground through the A/C compressor clutch relay control circuit only when the PCM or ECM
electronically pulls the circuit to ground.
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On gasoline engine applications, the coil battery terminal (86) receives battery current through a fuse in the junction block only when the ignition
switch is in the Run or Start position.
-
On diesel engine applications, 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 to the A/C clutch coil through the A/C clutch relay only when the A/C clutch relay coil is
energized.
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The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the A/C
clutch relay coil is de-energized.
The A/C clutch 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 micro-relay and for complete HVAC wiring diagrams.