Air conditioners create a lot of condensate when changing the temperature of your home. Usually this water is collected and flushed down a drain. When the air conditioner drains or drip pans are clogged with algae, dirt and debris build up, the unit will not drain properly, causing small puddles to appear. If you notice the leak is not water, but freon, call a service professional to deal with the problem, since freon leaks can be very dangerous to handle without the proper knowledge.
Inspect all the tubes connected to the air conditioner. Open the closet where the unit is sitting and check for any puddles beneath the tubing. Turn off the unit and place a bucket beneath the tub. Disconnect the tubing by unclamping it with a pair of pliers and replacing it. When checking a window AC unit, open the casing and inspect the tubing, removing and replacing in the same manner.
Lean down and locate the drain pan underneath the unit. Lift up on the drain pan to unhook it. Pour the water down the drain and clean the pan with diluted bleach to remove any possibility of algae forming.
Plug in a wet/dry vacuum cleaner and put the hose over the drain line which is located under where the drain pan was sitting. Suck the line with the vacuum nine or 10 times to remove the clog.
Pour a small amount of water into the drain pan and turn on the unit to test if it drains. The check valve may be malfunctioning if it doesn't. Unscrew the check valve, which looks like a ball and is located just before the discharge tube. Look for any obstructions in the check valve and clean it out if necessary.