Hymer Sunlight Van 1 purchase

I have now driven the van over 1,700 miles since Tuesday. Minnesota to Marquette MI in UP and now home to SE Indiana. I am pleased with it having finally had a chance to spend a night in it. Only problem I found is using the AC and invertor. We camped on Lake Michigan and when I went to use the microwave, I turned invertor on and then tried micro. It would not work and created a high pitched whine. I shut off invertor and then tried it again. Heard two beeps and then one beep and then I had a working microwave. So I tried the roof AC. Following same pattern it would start and then after 30 seconds kick off and the invertor area would whine. I know AC works as it was working on shore power, I know batteries have plenty of power and due to micro working I know invertor is working. So I put in an email to CW to have Ted in Monticello tell me what I am doing wrong. I have not tried plugging into shore power here at home because it has been too long of a day. Any suggestions, greatly appreciated.