Our 5er is set up for a 2nd AC unit up front including a 50 amp service and dedicated 20 circuit with 12 ga wire in the ceiling near the front ceiling vent. I'm thinking about installing the 2nd unit ...
When I did this to ours, there was a sticker on the junction box cover where the new AC was going, listing max amperage. So I had to stay under that. I put a 13.5k unit in, and that is big enough.