Electromechanical A/C Clutch Relay
Electromechanical relays are circuit protection and control devices used by the PCM and other sensitive circuits. They use an electromagnet (coil) that controls an arm that swings between two contacts. When low current is passed through the coil, a magnetic field is created that draws the arm towards the high current circuit. When the two contacts connect, high current is sent to the compressors clutch. This is a common (SPST) single-pole, single-through relay.
When low current is run through the coil, the armature or arm is pulled away from its park position to activate whichever high current device it controls. A standard has been developed for the plug of a mechanical relay. These include either four or five pins: 85, 86, 30, 87, 87a or 85, 86, 30, 87 (no park).
The relay uses numbers 85 and 86 as the electromagnet control. This coil will usually contain a diode to protect the contacts and other circuits from the sudden collapse of current when the switch is turned off. On these relays it’s important not to reverse the 85 and 86 (coil) pins. The number 30 pin is connected to the high current source and number 87a is the prong where the arm parks (off). The 87 pin is used to activate the desired device (on).