Trudy, on our thermostat the fan has a switch that reads on or auto and another switch below it that reads high or low for the speed. I would guess that you have the same thermostat because you have a 2010 PC just like me, unless you didn't get the conveniences package with the a/c upgrade.
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Tom, our PC is a 2006 and no matter how much I wish, it just wont turn into a 2010! For all the upgrades we've done, prob could have bought a new one! lol Anyway, all the thermostat has is a three speed fan - no "auto". Oh well, dat's the way it goes.