My Seneca had the same problem with the A/C's when I bought it a couple of years ago. I replaced the Coleman Mini-Mach's with full blown 15K Mach III's and never had any other problems.
I also have two Mach III's on the 24' trailer we haul with the embroidery machines, car and Goldwing. Nothing like being confortable in the Texas (or wherever) heat.
By the way, the coach electrical system is made so that the genset can be started, allowed a couple minutes to settle in, the load switched by the transfer switch and then the power cord can be disconnected.
But I believe that this causes too many arc's and sparks in the xfer switch. I normally shut everything down first, switch power and then restart A/C's, etc.
Lew