Blower unit doesn't tunn off
At night I want to turn off the air conditioning but sometimes the blower doesn't shut down. I know the central air unit is off but the blower continues. One switch is on Auto, where it should be, and I switch the other from cold to off but the blower continues. Someone told me the contacts could be dirty. It is an older unit. Is this something I can fix and how difficult would it be? Thank you.