An AC unit tune-up should be done once a year, generally at the beginning of the cooling season. There are some simple basics to AC maintenance that can and should be completed by every homeowner. Ardent DIYers will also clean the AC coils, but it's important not to over-reach. Issues with refrigerant and electrical systems should always be handled by a qualified HVAC contractor. 1. Complete an Initial Inspection: Check your outdoor condenser unit to make sure weeds or debris aren't obstructing or clogging the fins (the thin, vertical slats on the sides of the condenser). Likewise, make sure no cracks or visible damage has befallen the unit over the winter. This is also a good time to change your air filter if you haven't done so recently. 2. Give Your AC a Test Run: Lower the thermostat unit until your cooling system kicks on and let it run for several minutes. Check your outdoor AC condenser unit and the evaporative coil unit above the furnace unit. Make sure there are no strange noises, vibrations, visibly leaking fluids, or ice formation. Also, make sure the air coming out of the vents is cold. If anything is amiss, it's probably best to call an HVAC contractor. (If the contractor suspects it may be something very simple, he or she may be able to diagnose or even fix the problem over the phone.) 3. Complete a Basic Tune-Up: As a safety precaution, turn off the circuit-breaker. The first thing you'll want to do is return to the outdoor condenser unit. Check for bent fins. If needs be, straighten the fins with a thin stick or a special fin comb. If the fins are dirty, it can be also be a good idea to clean them with a soft, dry brush. And be careful: fins are thin-gauge aluminum that can be easily damaged. If the condenser unit has an external sensor, check the refrigerant level but if the air coming out of the vents during the test run was cold, it's probably fine. If the refrigerant level is low, call a professional. Finally, with a carpenter's level, check to make sure the concrete base and the condenser haven't shifted or sunk over the winter. A tilted condenser can lead to leaking fluids. Final Tip: Unless you're a DIY guru, a solid plan for AC maintenance is to complete basic maintenance on your own, but leave a more thorough inspection and cleaning to a professional HVAC contractor every other year or every third year, depending on the age and general condition of the unit. A professional contractor will be able to check your AC's electrical system, precisely measure temperatures and calibrate the thermostat, along with cleaning and inspecting components that may be inaccessible to the typical DIYer. By identifying when an electrical contactor needs to be replaced, for example, a professional inspection could save extend the life of your AC compressor and save you thousands of dollars."