I'm not sure what chassis you have, but I had exact same problem with my Ford F53 (Coachman Mirada) last week.
On mine, the dash AC system is provided by Evans. The fan would not work for heat or air, when I checked the fuses, they were OK.
When I stood on my head and looked under the passenger side of the dash, I found the blower motor resistor connectors, and the wire that goes to the blower from the resistor pack had overheated and fell off.
I cut tho old burnt connector off, installed a new spade lug connector, pushed the new connector onto the blower resistor pack, and BLAM, I was back in business.