In the past Airstream has used that circuit for the AC and Microwave with a switch in the cabinet close to where the Microwave would be installed at the factory. First test would be to turn the AC on and turn the circuit in question off and see if the AC goes off.
Newer units mat have separate circuits but the test will tell you if the is a seperate circuit for the Microwave.
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