The AC does force the fan on, but there are Low Pwr and High Pwr fan relays. The Low Pwr goes through a ballast resistor (I measured 0.7 ohm). I the 4-pin relays were in 'backwards' which made me crazy for about 10 minutes. They can go in both ways as the coil is on opposing corners and the COM/NO pole are one the other corners. Whoever installed them put them in 'backwards' according the the wiring diagram.