View Full Version : Adjustable Fan Thermostat to Relay Wiring Help

03-26-2006, 09:56 AM
Trying to figure out the right way to connect a relay to my adjustable thermostat for my electrical fan. Current set-up: Two wires from the fan; one to ground, one to adj. therm. One wire to adj. therm. from fuse box. The relay has #86 for (Switching Means), #85 for (Ground), #30/51 (Fused Power), and 2 #87's for lamps, etc. What is the proper way to connect this all together? Do I need to use #85 if the fan is currently grounded? Or even is using a relay for my fan even necessary if I already have the power fused?
Any help is appreciated.

03-26-2006, 10:42 AM
If it's working, just leave it as is. The reason to have a relay is to avoid large current flows through a wimpy switch contact. Think in terms of the starter relay, little 14 gauge wire closes the relay and 200-300 amps to the starter. If you have the wire big enough to handle the current and the correct fuse you don't gain anything by using a relay.

03-26-2006, 10:43 AM
The way you have it now somewhat defeats the purpose of a relay. The fan load still passes through the thermostat. The way I wire a relay is : 30/51 is main protected power, 87 is relayed power to the fan, 85 is switched power (green circuit) 86 to one side of the thermostat and the other thermostat lead grounded.There are some very low amp fans now that may not require a relay. The fans that I have installed in the past have a start-up load of about 26 amps then back down to a running draw of about 14 amps. The start-up draw is hard on the thermostat and I have seen them fail when they were straight wired. Also when running some aftermarket electronic ignitions , the system will back-feed and the engine will not turn off when the fan is running.

Alan T