try a can of coil cleaner you can buy at a local hardware store and have the drain line sucked out because all kinds of yuck builds up in them.
If you have a rainbow vaccum cleaner you can do it your self by just wraping a towel around the end of the drain tube and the hose to the vaccum to try to seal it while you are cleaning the tube out. Also you can put a teaspoon of bleach in the pan under the coils also. Use a soft brush to clean the coils with.