TD, after a bit of reading .....apparently the R-value (thermal efficiency) of AAC is 1.25 per inch thickness, a concrete block is 1.1/inch or approx 14% difference. Therefore (?) you should be able to use an air-con with 14% less BTU than is recommended in most of the online calculators which assume normal masonry construction. Is that logical ?
Hmmm ..wrong image attached but I cannot seem to delete it ? But it does compare an AAC wall to concrete block plus insulation, have to add r-8 insulation to match the AAC.