1997 Plymouth Voyager HVAC Control Head problem?

1997 Plymouth Voyager, 135K miles, HVAC fan comes on and goes off by itself. When I turn it on, it usually runs OK. Sometimes it won't come on at all, then starts up by itself as I am driving along. The little indicator light in the A/C on is on when it is supposed to be on. The fan has a mind of its' own.