I have a very common split A/C HVAC system. It has a 5 wire thermostat which I replaced recently with a new digital unit. (LUX9000) I have hooked up the wires according to the manual in a 5 wire system.
Y G W B R (AC Comp - Fan - Heater - Heater XFRMR - A/C XFRMR)
However, when I turned on the A/C, it did not work. So I switched the RH and RC wires.
Then it worked great. Then it got cold... and I switched it to heat... and not it did not work.
So I switched RH and RC back... and of course now the heat works.
I know I have done something wrong... but need help figuring it out. I have two 2.5 ton units that are identical... purchased 2 of these thermostats and wired them identically... and the issue is identical with both, so it is not a faulty thermostat or FAU. Please advise. Cheers: JP

Sorry but I have no info on LUX thermostats.

Look at your old t-stat.. did it have a jumper between RC and RH this might be the problem... just a guess since cannot see how the old was wired.

Jump Rc to Rh and it will be fine.