I wired my new thermostat all by myself and was very proud indeed. It works GREAT - there is only a little problem. If I want heat I must turn the thermostat to "cool" and if I want the a/c then I must turn the thermostat to "heat". I know that there must be two wires switched - but which ones? Unfortunately, this is an old house - and I did follow the instructions on the new thermostat - I am assuming that the wiring was not done with the correct color coding the first time around. Any hints?

Most likely the yellow and white are swapped. W and Y terminal...