Have a very unusual wiring configuration. Existing downstairs thermostat has white wire to white, green to green, red to rc and blue in the yellow slot. Yellow wire isn't connected at all yet the a/c works. When installing the nest learning thermostat I attempted the same configuration unsuccessfully. Tried installing the wires correctly: white to white, green to green, yellow to yellow, red to rc and blue to c. also tried the same configuration without connecting the common blue wire.
Upstairs thermostat was originally configured properly without the common wire and works fine. Just can't figure out this strange wiring for the downstairs unit. Original thermostats are honeywell and the system is Lenox inside and out. Electric a/c (house does have solar and not sure if that makes a difference) and heat is gas.
Help!!!
