A/C Compressor Clutch Relay: Operation

WARNING: This page is about a different car, the 2004 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.

The A/C compressor clutch relay is an electromechanical switch that uses a low current input from the powertrain control module (PCM) to control the high current output to the compressor clutch electromagnetic field coil. The movable common feed contact point is held against the fixed normally closed contact point by spring pressure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This electromagnetic field draws the movable relay contact point away from the fixed normally closed contact point, and holds it against the fixed normally open contact point. When the relay coil is de-energized, spring pressure returns the movable contact point back against the fixed normally closed contact point. The resistor or diode is connected in parallel with the relay coil in the relay, 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 compressor clutch relay terminals are connected to the vehicle electrical system through a receptacle in the PDC. The inputs and outputs of the A/C compressor clutch relay include:

The common feed terminal (30) receives a battery current input from a fuse in the PDC through a fused B(+) circuit at all times.
The coil ground terminal (85) receives a ground input from the PCM through the A/C compressor clutch relay control circuit only when the PCM electronically pulls the control circuit to ground.
The coil battery terminal (86) receives a battery current input from a fuse in the junction block through a fused ignition switch output (run-start) circuit only when the ignition switch is in the Start and On position.
The normally open terminal (87) provides a battery current output to the compressor clutch coil through the A/C compressor clutch relay output circuit only when the A/C compressor clutch 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 A/C compressor clutch relay coil is de-energized.

Refer to SYSTEM WIRING DIAGRAMS for diagnosis and testing of the micro-relay and for complete HVAC wiring diagrams.