How much power/electricity should my central air's blower fan use?
It is very unusual but not unheard of to have a furnace hooked up to a heat pump. Usually you would have an air handler and air handlers usually have backup electric heating strips. These heat strips Combined with the 300-400 watts from the blower could easily suck 1700 Watts. The strip heat should not be on when the fan is set to on and the temperature is turned down but it is not hard to miswire the unit. You should also verify the heat pump is not coming on too as this is not too hard to miswire either.