The 12,000 BTU A/C units require 10A service (15A breaker) at 110V. That means running 12 gauge (thick ~ 'calibre doce'~ ) cable for 110V units ...or 14 ga. cable (thin) for 220V.
Bigger air conditioners like 18,000 BTU draw 18A - 20A at 110V, (30A - 40A breaker), which would mean running (expensive) very heavy 8 gauge wire ... versus only needing 12 ga for 220V @ 10A for the same 18,000 BTU clima.
It's just not practical to build 18,000 BTU 110V A/C units, because it takes really heavy wire to carry the 20A current at just 110V.