Electrical question

Been a camper for a while, but relatively new to the RV style. 26" Class C (actually a Class B+). Pulled into our reserved camp site & set up. Slides out, leveled, water hooked up, plugged into electric (with EMS) and ready to settle in. Hotter than blazes so the air was turned on. After a few minutes we lost power. As I frantically ran in circles and turned off the air & everything else I could find the power came back on. I thought that's great. Then I looked at the EMS and saw an E2 error code. Open ground. Being electrically stupid, I thought good it foud the problem. All was clear and up & running. Turned on the air again and within a few minutes it happened again. Not knowing what to do & ringing wet from the heat I removed the EMS and plugged directly in to the power poll. All worked fine.
Was I just dumb & lucky or what. It was far too hot to do without air as DW & I are asthmatics & have respritory issues. It was getting later in the day & campgroun was full so no place to go.
Was this a totally wrong move on my part or what should I have done?

thanks