Well I donít know your coach specifics at all, but until an expert HVAC person responds to your post I have a couple comments:
1. I hope the mobile RV tech wired your blower fan with appropriate sized wire and fuse for the blower motor load requirements and advised you where (at the chassis battery) he placed the fuse? Not the preferred solution to say the least.
2. I suspect (but I am not sure) that many RVís still use a combination of electrical switches and vacuum operated control motors to provide the HVAC dash requirements. Usually if there is a vacuum leak or failure the default is to go to defrost air flow position. So it could be a vacuum hose cracked or pinched somewhere in the dash. This typically requires opening up the dash for access/inspection. Maybe this will allow proper repair of your blower motor too?
Some interesting reading after doing a search on the forum......