Hi, I have a '91 S-10 4.3 L 2WD. I need to know which terminals on the A/C relay are the power terminals. The larger ones or the smaller ones. Thanks! Kevin

 

Pop the cover off the relay and see which terminals connect to the coil of wires inside.
If you can't open it, use a couple of wire jumpers, one to a 9-12v positive and one to a 9-12v ground (a good flashlight battery or 9v battery should suffice) Then jump the terminals. Start with one terminal at random. Hook it up to the - terminal. Jump each of the others to + terminal one by one.
If you don't hear a click (the relay switch engaging), its a power terminal. Go to the next one and so on until you figure out which ones are power and which are control.


Relays are automatic switches that allow closure of a circuit without running high amperage through the manual switch. There is a coil of wire inside the relay that creates a magnetic field when a low amount of current is applied to it via a manual switch. The magnetic field pulls the contacts of the power circuit closed, completing the circuit to the power accessory. When the control circuit is de-energized, a spring opens the power contacts and cuts power to the accessory.