If wanted to make the room to be cool, rules no.1 prevent cool air to leak outside the room else the compressor will keep on running. So in this case it will utilize more power.

This post has been edited by HonMun: Sep 9 2011, 10:17 AM

More Efficient Air Conditioning:
One of the most inexpensive and effective ways to reduce your air conditioning costs is to adjust your thermostat setting. The savings can be significant when you set your thermostat at 78 degrees Fahrenheit or higher. For each degree you raise your thermostat setting, you reduce seasonal cooling costs by 6 to 8 percent.

Setting the temperature a little higher of around 78-80 degrees Fahrenheit , will you save 6 to 8 percent of your cooling costs for each degree above 78, and most people will be comfortable.
Use a ceiling fan or portable fan to supplement your air conditioning. A fan can make you feel three to four degrees cooler (and only costs a half-cent per hour to operate) so you can set your thermostat a few degrees higher and save on cooling costs. Use in occupied rooms since fans cool people, not rooms.
Turn off the air conditioning or set the thermostat up a few degrees when you leave home.
Be sure your air conditioner is not blocked. A free flowing air conditioner operates most efficiently Be sure the return air grill inside your house is not blocked by furniture or other items. Filters should be checked monthly.
When air conditioning is on, keep doors and windows closed Turn off kitchen or bathroom exhaust fans when your air conditioning is operating.
Caulk and weather-strip leaky windows and doors.
Shade your home from direct sunlight. Use shades, drapes, awnings, trees and shrubs to block the hot sun from heating up your home.
If you suspect your air conditioning system is not cooling properly, have it checked promptly. A unit that is having operational problems can cause extremely high bills.
If your air conditioning equipment is older and less efficient, compensate by being extra careful about temperature settings, hours of operation and filter condition.

Biggest Money Saving Improvements
Four tips to provide the greatest energy savings:

Replacing an old air conditioner with a high efficiency unit
(new air conditioners use up to 40% less electricity than older models)
Sealing leaks in ductwork in your attic
(the average home loses 15%-25% of cooling and heating through leaking ducts)
Adding attic insulation to R-30
(the average 15-year old home has between R-11 and R-15)
Installing solar screens or awnings on windows hit by direct sunlight
(solar screens reflect back 60%-70% of sunlight/heat before it can enter the house)