Most of the time when water leaks from an air conditioner on the floor the drain line is stopped up. I use compressed air or a wet vac to try and unstop the drain line. Water leaking can also be caused by a leaking coil drain pan. The evaporator coil sets in a drain pan. If the pan rusts out and gets holes in it, it will leak. You or the service man would need to inspect the coil to see if the drain pan is leaking. This can be difficult and time consuming since the coil is usually cover up with sheet metal and you need to look under the coil bottom. This may be why your service man says you need a new coil. The coil drain pan is hard to repair and you usually have to take the coil completely out to repair the leak. Water on the floor can also be caused by a coil that freezes up or forms ice. This condition is usually cause by a low refrigerant charge, but can also be caused by a stopped up filter, dirty blower, dirty coil or a motor that is dragging (going bad) and not producing enough air flow. A weak capacitor could cause a motor to not run up to speed.