I think you missed a 0. I've never heard of an AC unit for a house that's 400W. 4000W and above is more common.

Google:

> An AC unit's electricity usage varies by type, with window units using around 500–1,500 watts and central air systems using 3,000–5,000 watts, though usage can range from 2,000 to over 6,000 kWh annually for central units

Also, how much you use it during the year can vary hugely from 0 (when I lived near the coast) to like 10 hours a day for months in hot or cold places. There's not a standard, but 55kwh for a year means you live someplace that doesn't really need AC / heating.