Before attempting any repair, unplug the AC.
First, you want to check that you even need a repair! Make sure your thermostat isn’t on ‘cool,’ ‘energy saver,’ or auto mode. You should be able to switch it off while the unit is running.
Replace your filters every month and clean them every 2 weeks. Clean your coils once a year using a brush attached to an extension rod. If there is no light in the closet, masking tape and mark the filter to know where it goes when you replace it.
Make sure the unit is level, as this will improve efficiency and cooling capacity.
Check your ductwork. If there are any leaks or holes in the duct-work, this causes a lot of loss both with airflow and heat transfer. Leaks can also be found where the supply and return air come together. Also, check for open seams where the foil insulation isn’t holding on anymore, which is common in older units that use tape instead of foil tape to seal seams (which makes future repairs much easier).
The Evaporator Coils
Check your evaporator coils for mold growth around drain pan areas. This happens when water drips down from the compressor tray due to an improper installation.
The Electrical Connections
Check the electrical connections for proper voltage (should be 220v, single-phase). Also, check for rust or corrosion on wires and terminals as well as loose connections.
On gaseous heat systems, clean both dryer and condensate drain lines. If you have a gas furnace, make sure it is serviced every 2 years by a professional. Clean the burner components (if accessible), both the venturi tubes and burners themselves regularly, to ensure efficient combustion.
Make sure all windows are properly sealed with insulated drapes where needed. A quick way to check is to use an incense stick and hold it over your registers in each room while someone watches outside through an open door. If the smoke doesn’t hang in a straight line, you have air infiltration and need insulation or weather-stripping.
Check that all air registers are open.
Check that there is good airflow throughout the house by feeling registers and check for proper temperature on return ducts (should be between 50°F – 60°F). Finally, check for any possible broken parts around your unit (sound like they’re about to break when you shake them)?
After doing all of the above, you’ll probably need a new part if everything looks fine. If the problem remains after doing all this, though, then it’s time to call an ac repair professional!