If the fuse is blowing when you set the system switch to cool you are narrowing down the cause. You stated you disconnected the leads to the condensing unit coil. Did you disconnect them at the furnace control board or at the outside unit? If you disconnected them at the outside unit the leads are probably bare and touching somewhere between the furnace and outdoor unit.When you energize the contactor coil for the outside unit, there goes the fuse. Mice or a whacky weedeater operator are usually the culprits.