Hello, I have a house with multiple HVAC systems:
A boiler in the basement has two zones for main floor and upstairs floor.
A central AC in the attic has one zone for the main floor and upstairs floor.
A furnace in the basement has one zone for heat and AC for the finished basement.
I replaced the prior "dumb" thermostat that controlled the whole house AC and main floor heating that was in the family room with an Ecobee a few years ago.
Recently the ancient "dumb" thermostat in the bedroom that only controls the upstairs heating broke. It is a Honeywell 97-4730 Rev A.
Looking at the wiring, I saw an unused wire in the wall. I checked with a multimeter and it drew 27 volts between the wire and the R wire, so I believe that is an unused C wire.
In the Honeywell, there are wires plugged into R, W, and Rc. There is no jumper wire.
The new Ecobee Enhanced I bought says the wire combination is not compatible. Is this because there is an Rc but no Y? The thermostat does not power AC so why is there an Rc? Can I cap off the Rc and only use R, Y, and C?
Thank you for your help.