'70s model airstream camper AC....

it could be a relay or resistor for the fan that has burned/shorted out. can you tell if the compressor kicks on when you turn the a/c system on? what about by-passing the entire system and making sure the fan does actually run by disconnecting the fan leads from the system and depending which voltage it is, connecting the appropriate voltage to it and ensuring the fan works. if it doesn't run, the try another fan of similar current/voltage draw and connect it to the system and see if it runs accordingly. if it still doesn't run, the back track you wiring within the system and see where the leads run to, leading away from the fan. there may be a relay or something similar that won't energize if the compressor doesn't kick on. if the compressor kicks on, but fan doesn't work, its a problem between the compressor relay capacitor/relay and the fan relay