I just moved into a new house and the digital thermostat is not working as I expect.

When I turn the heat/cool swith to "off" and the fan switch to "on", the blower on the central air unit outside kicks on, but the fan in the inside unit does not.

When I turn the heat/cool switch to "cool" and the fan switch to "on", both the blower and the central air unit kick on.

I assume it is wired incorrectly, but before I pull the cover and start messing with wires, I want to see if my assumption seems correct or if there are watch-outs I need to be aware of.

Thanks

Sounds like the wires are backwards. G and y probably.

The fan also kicks on when the furnace runs. Would that still be the case if g and y are backwards, or would I be seeing the outside AC unit kick on when the furnace runs?

Does it come on as soon as you turn it to heat? Or after a breef time? Also if you turn everything to off and the fan to auto will it shut off?

I think that you are correct, that the wires are backwards. If I turn it to heat and fan to on, the AC blower kicks on. I have to turn the fan mode to auto for it to kick on in furnace mode and it does so immediately.

What brand furnace do you have and is it gas, or electric heat?

A gas Trane

Turn off the power at the furnace, take the t-stat off the wall and let me know what wire is where?

Figures.

With conventional heat, the furnace controls the fan in heat mode.

In cool, the thermostat controls the fan. (g and y energised at the same time)

Fan energises G.