Alright I had the same problem and after using checking voltages I found that it was in fact the resistor. However the physical resistors on the unit seem fine so I was wondering how the switch thing mounted at the bottom of the board worked and if it could be repaired. Maybe I'm being cheap but it doesn't seem like anything else is broken and I already cleaned all the contacts and whatnot so that's the only questionable part left.
EDIT: In general if number four works that means you have full voltage to your blower motor. The resistors are on a separate circuit which generally means a bad resistor. If say 1 or 2 out of the 4 work then it would more likely be the switch.