My cooling and heating system has four wires: white blue green red rth3100c1002 --0801 contacts: E Aux Y G O L R B C -- Optional My connections: White wire to AUX Green wire to G Red wire to R Blue wire to B Result: Fan works in the on position. Fan comes on the the auto position when the thermostat is set on cool and the air rises above set temp, but no cool air. I have not tested the heat position.