Be sure the insulation covering your coolant line, from the condenser to the compressor, is still in tack. Accidental removal of the insulation combined with use can cause lines to freeze. Animals are often to blame for removing the insulation to outside units.
Evaporator and condenser coil fins need to be kept straight. To straighten the fins a special comb can be purchased called a fin comb. Bent fins will limit air distribution throughout your unit.
Inspect your outdoor units often for vegetation or foreign materials restricting the airflow. Eliminating direct sunlight to the unit also helps improve its cooling efficiency.
Filters play a major role in how long your AC will last. If they are blocked, they will place extra strain on your system. Replace filters monthly, or quarterly based on the filter you may have purchased.
Be careful to never set the unit below 65 degrees. This could cause freezing of the lines, which can ultimately cause an outage in your system.
Keep all air conditioning vents free of obstructions. A blocked return reduces air flow, which can cause your system to freeze up.
Check on circuit breakers and fuses. Circuit, when overloaded, can easily switch off. Commonly used appliances such as refrigerators, microwaves and irons can cause the overload.
Make sure the unit is getting power. Is your thermostat working properly? Is the unit plugged in?
Check the thermostat current temperature. Especially now, in the days of programmable thermostats, your temperature settings may have become reset.