How an air conditioner works
An air conditioner is a device which cools the indoor air by removing heat and depositing it outside. It circulates indoor air and does not bring outside air into the home. A filter in the return air duct is required to keep the air conditioner clean and operating efficiently.  AC units are rated in BTU’s (British Thermal Units) of cooling capacity. As a rough rule of thumb, 1,000 BTU will cool 40 to 50 square feet of well-insulated space with few windows providing that the room is approximately 8ft tall.

 Factors that affect the cooling capacity of an air conditioner

1. The average ambient temperature of your area during the year
   
   
2. The higher the average temperature of the outside air, the more will be the cooling capacity required.
   
   
3. The size of the room
   
   
4. The cooling capacity required is proportional to the area of the room you wish to cool.
   
   
5. Coming shortly
   
   
6. The more the number of people present, the higher will be the capacity required.
   
   
7. Exposure of the room to sunlight
   
   
8. Direct exposure of any of the walls of the room to sunlight, would lead to higher requirement of cooling capacity.
   
   
9. Proximity of the room to kitchen. If the room is nearer to the kitchen the cooling capacity required would be higher.