A/C Compressor Clutch Relay: Operation

WARNING: This page is about a different car, the 2004 Dodge Pickup and 2004 Dodge Cab & Chassis. 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) or engine control module (ECM) depending on engine application, to control the high current output to the compressor clutch electromagnetic 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 integrated power module (IPM). 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 IPM through a fused B(+) circuit at all times.
The coil ground terminal (86) receives a ground input from the PCM/ECM through the A/C compressor clutch relay control circuit only when the PCM/ECM electronically pulls the control circuit to ground.
The coil battery terminal (85) receives a battery current input from PTC 1 in the IPM through a fused ignition switch output (run) circuit only when the ignition switch is in the 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 the appropriate SYSTEM WIRING DIAGRAMS article for diagnosis and testing of the micro-relay and for complete HVAC wiring diagrams.