Open all of the shades covering the windows in the sunroom. This will allow the sun's light to enter and heat the room.
Turn on any heat that you have operating in your home. Open the air vent in the sunroom.
Close the door into the sunroom. Fully compartmentalizing the sunroom allows the sun to warm the room more quickly and efficiently.
Turn on your central air conditioner and make sure the air vent to the sunroom is open.
Close the shades on the windows in the sunroom. This prevents the sun from heating the room any further.
Open the door from the sunroom to the other parts of your house. This will allow for better circulation of the cool air from the rest of your house into the sunroom.