1) Unplug the unit and carefully remove it from the window. Put it somewhere outdoors where you can work on it.2) Remove the grille and filter and unscrew the metal case (do not damage the coil’s fins).
3) Wash out the filter or replace it with a new, inexpensive filter—cut-to-size foam filter fabric is available at most appliance stores.
4) Using a vacuum with a soft brush attachment, clean the inside coil’s fins.
5) Then, from the fan side, spray water back through the fins (protect the wiring and motor with plastic).
6) Clean the unit up with a rag, making sure all drains that allow condensed water to drip away from the unit are open. Allow it to dry thoroughly.
7) While you have the unit apart, lubricate the motor according to your owner’s manual’s instructions.
8) Then reassemble and reinstall the unit.
If that doesn't do do the trick, clean the evaporator and condenser coils.
