Being well into the cooling season, I would like to share a few useful air conditioner maintenance tips. An efficient system should have a temperature difference of at least 15 F between the return air and conditioned air - this can be easily measured by an infrared thermometer. If the difference is less, or significantly less, the unit needs maintenance. A good option is to call a licensed A/C tech, who can address any and all problems at once, then have him return every 3-6 months again for regular maintenance. Even in this case the homeowner will have to change/clean the filter at the required intervals, making sure that the correct sized filter is being used. Since the heat from the house is dissipated outdoors, it is crucial that the airflow around the outdoors unit (condensing unit) is not impeded by vegetation, debris, etc. If the clothes drier vents next to the condenser unit, the lint must be cleaned off the coils frequently. The "Cool-Cap" is a useful invention, that prevents rain and debris from getting in the condenser without impeding the air flow. The refrigerant lines sometimes have deteriorated or missing insulation, this should be replaced. A do-it-yourself project can be to assess and clean the evaporator coils. Access to it is usually inconvenient but possible trough the return grill or other ways. The clean coils have a metallic shine, the dirty coils can have gray/black/brown debris on the fins, made of lint, hair, dust and mold. They can be cleaned with coil cleaner and a soft brush to improve cooling efficiency. It is recommended to pour a cupful of bleach into the condensate line twice a year to prevent it from clogging. A small, but helpful investment can be a "Safe-T-Switch", a switch installed into the condensate line that shuts off the system if the line is clogged, preventing an overflow of condensation. If a system equipped with the "Safe-T-Switch" stops cooling, it is worth looking at the switch before even calling out an A/C tech, as in many cases the clogged condensate line is the root of the problem. Once the line is drained, the system resumes operation. For any other maintenance or repairs please call a qualified A/C tech who is trained and equipped to safely perform any repairs.