1996 E320 A/C Heat Fan

[USMCR O-5]

The blower fan in my 1996 E320 has been working sporadically for a few months now. Sometimes it comes on immediately after I turn the car on. Other times, it will not run for several days. There seem to be no pattern to this. No matter what I set the fan or temperature to, it seems to have a mind of its own. It's still pretty hot here in Florida and I really would like to have the AC blowing. Any help would be appreciated.