If it is a 13,500 BTU air conditioner it will take about 23 amps to start it, once running it will take about 15 amps. It's likely your converter and a few other loads will be running at the same time. I could run my 13.5K AC on my old unit at home on a 20 amp breaker, but it was a stretch on startup. But I only did that with no other loads and for short periods of time. And if you plan on running the microwave at the same time it definitely won't work. In my opinion, for long term use (more than a couple of hours), 20 amps just isn't enough. If it's a 15K Air conditioner, you'll definitely need the 30 amps.