Arrived to find system running in cooling mode when calling for heat. Inspected system to find 24v to “O” wire only outside and not at air handler. Assumed only that the wire has been nicked and that it’s getting a constant call from another wire running in it. Gave client option for labor to switch wiring or to replace wire from air handler to condenser. Rewired condenser and tested heat and cooling modes to assure proper functions. All is now working as designer.