1. Wash the filter.
The main thing to do to upkeep your window unit is to make sure you wash the filter screen on a regular basis. After popping out the front grill of the unit with a putty knife, remove the mesh filter. Wash it together with the grill in a mixture of warm, soapy water and bleach to remove any mold.
2. Clean the coils.
You'll find evaporator coils underneath the filter. To keep your A/C going strong, you'll want to vacuum them thoroughly using a brush attachment. Remove any stubborn dirt with a plastic scrub brush. Do the same thing with the condenser coils at the back of the A/C unit. The idea is that extra debris gets in the way of air flow—an your cool air.
3. Straighten fins.
Use a fin comb to straighten any bent coil fins. You can find fin combs at a home or hardware store or online for around $10.