the controller has one adjustment knob. it controls both fans. first one comes on at your set temp. 2nd comes on 10-15* hotter. both shut off when the fall below the set temp you choose for first fan. also have a manual override switch that will turn on 1 fan. I have a switch set up that is run between the sending unit wires so that if i hit the switch both fans come on and stay on. this set up with both fans going will cool the car from 180* down to below 160* and close the thermostat. I am extremely happy with the set up.
