Since replcing the termostat, my AC compressor fan runs when the furnace runs. This never happened before I replaced the thermostat. What did I do wrong with the thermostat replacement?

It sounds like you hooked the compressor control wire to the wrong screw. It is usually yellow, or at least the screw is marked Y. Without knowing what you have now, it is difficult to say what is wrong.

Hope this helps,
WallyH

The Blue wire was incorrectly hooked up to the B terminal on the thermostat. When I traced the Blue wire to the furnace it was connected to the Y termainal in the furnace, when this change was made on the thermostat, it is working correctly again. Many thanks