Nest 3rd Gen wiring for seperate Heat and AC Air Handlers

[Paul_Mc]

I just bought a Nest thermostat and I am trying to figure out how to wire this up correctly.  I have and Air Handler in the attic for a HE 3.5 Ton 17 seer AC unit and then I have a seperate Gas Froced Hot Air furnace in the basement for heat.   I had a totaline thermostat that was controlling both units.  I have an isolation transformer on the basement unit.  The AC unit in the attic has a 2 stage air handler.  The way it is currently wired the AC unit works as expected both stages.  However when the heat is calle for both of the units fans come on.  This is not optimal and was not the case with the old thermostat.  I searched online but could not find any wiring diagram for this sepcific situation.  Lots for hot water base board heat and AC.  Any suggestions here would be apprecited.

Thanks

[Paul_Mc]

Well I figured out a work around.  This Nest was a replacement for one that the wireless radio went bad in.  I have to say Google stood behind their product like no other company I have dealt with kudos for that.  I think the replacement has a setting in the Pro area that controls whether the Fan is energized by default when heat is called for.  I can't get to that so I am unable to verify my assumption.  Any way I was able to wrok around this by going into the equipment area and selecting the Radiator option.  Obviously if you have radiators there is no need to run the fan so the fan in the AC air handler in my attic no longer comes on but when heat is called for the furnace in basement kicks on and the fan is automatically turned on by the control board in the furnace.  Voila now it works as expected.  It would be nice to be able to verify the Pro settings somehow but I understand why this is tightly controlled.