No, the blower resistor problem is when the fan works on 4 but not lower speeds.
Just a goofy suggestion, try turning on the AC, but turn off everything else electrical in the car that you can turn off, radio, lights, etc. See if it works on the other speeds then. If so, check your battery cable terminals, and the connection at the alternator- with the negative terminal removed from the battery of course so you don't go spark spark OH CRAP.
Another thing you can try is swapping the AC relay with the headlight relay. The two relays should be the same, but I don't think the AC turn on circuit is wired in with the fan. That would be weird, but not unheard of. I don't have a wiring diagram to verify.
If you verify that voltage loss is not the cause, then I'd guess the fan switch, not the resistor, is the problem.