For what it's worth, i have a Hong knockoff of a FantasticFan in our unit. It came with only one speed and direction. I found a 6 ohm wirewound resistor rated or 25 watts- a big honker. I replaced the old single pole switch with a SPDT switch. One side runs straight voltage for high and the other side goes through the resistor for low. Since the resistor does get warm (but not hot), i attached it inside a small steel pancake fixture box which not only protects the RV from the heat but also acts as a heatsink for the component. Just like that, I have a two speed fartfan. It consumes nearly half the current on low too (about .7A) - despite the resistor warmth. Perfect for remote boondocking. But I wasn't done! I also added a DPDT switch which i cross-wired to enable instant fan reversal. Why reverse an RV fartfan to blow in? Because when you flush the can with the fan sucking air out, much of the air it sucks up is drawn out of the biffy and brings with it that wonderful black tank aroma. That's why! I also didn't want to use an oscillator circuit which was suggested here as that tends to cause radio interference.
