If the trailer sat for a time the blower shaft may be stuck. Not sure you can get to it from inside but take a look. If you can try and spin the blower. If it spins freely the motor may be shot or just not getting power. To check power you will have to get to the motor wiring and test for voltage while the AC is on. Keep in mind that is a multi speed motor so there will be at least 4 wires going to it.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles