Fan control relay operates solinoid to run fan, (rated at 80 Amps full time). A solinoid is needed because fan has 100A start current and 33A running current, control contacts are only rated at 30 Amps. Also note diode to shunt voltage spikes to ground, (generated by the inductive fan motor when it is shutting off).

Owner caption September 2008 · Photo 74 of 336