Why does the furnace fan still run even after air conditioning has reached its coolnest? And what is the switch for on the furnace?. my temp in the house is 70 and control set on 70 but furnace still runs.. what happen if I turn the switch off on the furnace?

What brand and type is the unit you have?

:)

The furnace is a Payne... and I'm learning how to set the thermostat, & that is a lux wx500