Hi, we recently installed a window version of a swamp cooler. As such, it plugs into a wall outlet in the lounge-room. It has a new 1/3-hp (252-Watt) two speed motor from HomeDepot.

When it turns on either in Low or High, the voltage dips for almost a second from 125vac to 117vac then back up to 125vac. The dimming is maybe 20% longer for the High speed.

Is there some way we can soft-start this or what? It makes the lights dim in the house for that short period.

Before anyone launches into "house wiring," etc rest assured it is 11-years old, copper, in metal conduits and all up to code with 200-Amp coming into the house.

I used a 14g, 3-wire extension lead in a bunch of other outlets on different circuits and still get the same issue. I then hard wired the extension into the main breaker panel. Same again.

I have cleaned and oiled the fan bearings, adjusted the belt and the fan turns quite freely by hand.

What can be done to alleviate this momentary voltage drop?

Thanks