With a central air conditioner that runs through ductwork, the most important thing to do is change the furnace filter. Replace the filter about once a month, depending on how often you use the system and if you have pets that shed.
Trim back any vegetation growing around the exterior condenser and brush off any leaves or other debris on it. A couple times a season, you should hose it down to rinse off any dust or pollen that’s built up on the coils or fan blades.
If you have a window-mounted or ductless A/C unit, there is a filter on the inside that you should remove and rinse with soapy water. Make sure you allow it to dry completely before reinstallation. On the outside, hose off the coils on the back of the unit as you would with a central air system.
You can improve the efficiency of your system by blocking off the vents in rooms that you don’t use very often and closing the door to those spaces. Blocking vents also helps prevent small spaces, like a power room, from turning into an ice box. You can also close the blinds on south-facing windows during the day to minimize the amount of solar heat entering the cottage.
Over the course of a day, hot air builds up in an attic, which then seeps down through the ceiling at night. Make sure your roof has sufficient vents to circulate the air as much as possible, and consider adding some extra batts or loose fill insulation to provide a barrier.
If you notice that your system just doesn’t seem to be cooling the place off, the coolant may have leaked away. In that case, you’ll need to book a technician to service your machine.