First check your thermostat. Is it set to fan? This will make it run all the time. Next Check the wiring to the thermostat - if miswired will do the same. Now check the furnace wiring - schematic documentation for furnace should help. When set to air, furnace maybe wired to have fan run constantly. If you can not find the problem, get a "GOOD" HVAC technician - not a salesman or installer. Someone who understands the wiring.