Not to get into an A/C class, but have you any means to measure temperatures directly at the AC? For instance, can you measure the temperature coming directly from the AC either at the closest vent, or if you have the cool dump feature, open it and take a supply side measurement. This should tell you if it is working at all and if it is, with continued monitoring you might find the compressor cutting off and with the fan continuing to run, you might think it is "on". Also, A/C does two things, remove humidity and cool the air. If you are in a high humidity area, getting indoor temps down can take a while. If you find the compressor is cutting out while the fan is continuing to circulate warm air, you could have a bad run capacitor, bad compressor, or low refrigerant charge.
I have a 36 foot 5'er with two A/C's one 15K BTU and one 30K BTU. Even with both of them on, it takes a while to cool down. Especially since the DW like to have the door open. Have you considered another AC?
John & April & "Scout"
Nights Camped 2013-(44)
Nights Camped 2015-(47)