Here are the facts: Hot air rises. Cold air sinks. Window unit air conditioners are designed to cool a room or two, depending upon the size of the AC unit and the size of the rooms you are attempting to cool. Central air conditioning cools an entire residence with fan vents to every room. You cannot circumvent these facts and there is no adjustment on any known window air conditioner to cause cooled air to rise to the ceiling of a room or the upper story of a house.
Steps:
Move your window AC unit to an upstairs location. Cold air will still flow down to the lower floor but you may gain some comfort and cooling as it rolls down the stairs. A long curtain hung — if possible — at the stair entry will slow the cooler air from settling downstairs.
Invest in a quality ceiling fan or two, with at least one upstairs. Ceiling fans won’t cool the air but they will help air circulate and make you feel cooler by almost 5 degrees. Depending upon the direction in which it rotates, it can either pull cooler air up or push warmer air — temporarily — down. If this option is too expensive, try a couple room fans.
Consider installing an attic or roof exhaust fan. This option is expensive, but will remove the hottest air from your attic area and in turn, pull the hot air from your second story.
Tips & Warnings
Use shades and curtains to lessen the heat from sun-facing windows during the day.
Always use an appropriate outlet to plug in a window air conditioner. Never use a 3-prong-to-2-prong adapter as this may overheat your home’s electrical wiring or the AC unit.