The o4 Adveturer came staandard with 30 amp and 5.5 onan genset. It had an option for 50 amp and 7.0 onan genset. Also Powerline EMS.
Based on your discription and the statement by the tech, your EMS is cutting power to the electric water heater. My EMS shuts power down in the order of
1. Water heater
2. AC compressor 2
3. Fan speed (I assume that meand also AC compressor 1)
4. Refer. (Refer automatically goes to LP if that happens.)
You can test this out by starting your genset and then watching the amps increase as you add items. I would start with refer on LP then add electric water heater (you may need to run the hot water to make sure it is cold enough to start up), then add refer on electric, finally add AC. You will need to make sure you set the thermostat so that it is at least 3 degrees colder than the curren temp to get both compressors running.
As AC 1 kicks in, you should still have 4 green lights on your EMS showing everything available. When AC2 kicks in you MIGHT see the electric water heater light go out on the EMS. If your buld hasn't blown out on the electric water heater switch (like many do) is should also go out if your EMS has taken it off line. CAVEAT...I have a 50 amp EMS and your 30 amp EMS might be slightly different in how it sheds devices.
If you EMS also reads out amps in use, you can learn how many amps any item draws simply by running your genset or being plugged into snore power. Then turn on various items in your coach to see what they draw. For example, a hair drier will generally draw about 10 amps! This will NOT work if you have a 50 amp coach and are plugged into 50 amp service. In that case, you will not see any information on amps in use.
Don, Sandee & GSD Zeus. Guardian GSDs Gunny (7/11/15) & Thor (5/5/15)
2006 2015 DSDP 4320 4369, FL Chassis, 2013 CR-V 2020 Jeep Overland, Blue Ox Avail, SMI AF1.