[cdc_carter]

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

[Joshdta]

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

[cdc_carter]

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?

[Joshdta]

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?

[cdc_carter]

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.

[Joshdta]

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

[cdc_carter]

A gas Trane

[Joshdta]

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

[KISS]

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.