Here is how this circuit works. This circuit has one relay, a refrigerant pressure switch, and a micro switch. The micro switch is a W O T or wide open throttle switch used to disengage the compressor clutch during wide open throttle conditions. How To Test A Relay And The Relay Circuit.How do you know if your problem is really your battery? How do you know when it's time for Don't overlook relays, switches, wiring, and solenoids in your search, too. A parasitic draw may also be at the root of Remember too that a battery that is only just passing these tests is likely to get worse quickly.[Compatibility]: The A/C clutch relay fits for many Toyota vehicles, including 2003-2014 4Runner, 2002-2011 Camry, 2007-2011 Camry Hybrid, 2007-2014 Tundra, 2004-2013 Highlander and more vehicles, please kindly check the fitment model on follow description. Apr 27, 2017 · Using a multimeter. The only tool required to check a relay is a multimeter. With the relay removed from the fuse box, the multimeter set to measure DC voltage and the switch in the cab activated, first check to see if there are 12 volts at the 85 position in the fuse box where the relay plugs in (or wherever the relay is located).