The room air conditioner is like an entire house cooling system in one small package. There are the same components just shrunk down for the reduced duty of cooling a room instead of a home. There are "inside" and "outside" components to the room air conditioner.
Located inside the home you'll find components designed such as the evaporator coil (the one that gets cold), the fan or blower to blow cool air into the room, the thermostat, some type of filter (usually foam) and the plastic face panel.
Then there is a panel that separates the inside equipment listed above, from the equipment components located outside the window. These exterior components include the compressor, the condenser or condensing coil (looks like a radiator) and the condenser fan to blow air across and cool the hot condensing coil. The moisture condensate from the evaporator coil (inside component) drains along the bottom of a metal pan and drips to the exterior through a hole or condensate drain tube.
The whole package is neatly housed in a metal enclosure and sits partly in and partly out of your room's window.
Now let's take a look at some possible problems you may run into and how to fix them.