I'm working with a dual fuel setup: Lennox HP with a gas furnace to run as the auxilary. Originally, there was a standard hp+aux thermostat (with the furnace set so it would only run if the user switched the tstat to "emergency"... this prevents the hp and furnace running simultaneously.
To improve efficiency, a dual-fuel tstat was installed, but since then, the hp will not run at all, even when the original tstat was reinstalled... but rather, when the compressor (Y) lead is engaged, the furnace turns on only. (Of course, this occurs when the aux (W) lead is engaged).
what would cause this?
thank you to anyone to can help!