Have you ran this combo before? Just a guess here but did you start them in that order? The A/C will draw a bunch of power when you start it up then it will need less voltage when running. Someone was mentioning last week how much it takes for a coffee maker to run off his inverter, I was surprised.
2015 Tiffin Phaeton Cummins ISL, Allison 3000, 45K GCWR
10KW Onan, Magnum Pure Sine Wave Inverter
2015 GMC Canyon Toad
Previous camping rig
06 Ram 3500 CC LB Laramie 4x4 Dually 5.9 Cummins Smarty Jr 48RE Jacobs brake
06 Grand Junction 15500 GVWR 3200 pin