What would make the heater stop blowing while on, and intermittly start and stop blowing (days apart)?

This is a 1979 Bill Blass signature edition belonging to my father. He had the blower motor replaced a year ago and about three weeks ago early in the morning, he had the heat on while driving. All of a sudden, the blower stopped working. Then the following day, it worked again. Yesterday he called and said it won't do anything again. I checked the fuses,and the wiring (that I could reach) for loose connections, but came up with nothing. I'm not sure of the exact wiring and relay setup on this car and could use some help. I'm currently out of work and can't afford to bring it to a shop for him. It's getting cold here and he's 84 years young. please steer me in the right direction to help him out. THANK YOU!!!