Residential Air conditioning Repair and Maintenance Tips you can do yourself.

These are steps you can take when getting ready to start your A/C or mini-split Heat pump at the beginning of the warm season.

• First turn the central air system off on the thermostat.  In the case of heat pumps, the outside disconnect will de-energize the whole system.
• Keep weeds and grass away from the outdoor condensing coil.  I prefer to put stone or mulch around the base to keep it that way.
• Inspect the electrical disconnect box, as well as the flexible electric conduit for disrepair. You should turn off the unit at the outside switch or pull out the handle to be sure the power is off before cleaning the unit.
• There are two refrigerant lines, the larger of the two is insulated.  The insulation can be patched with electrical tape if its not to decayed, otherwise you can replace the short section of insulation if you are comfortable doing it.
• When the AC is running, the larger line will probably be "sweaty", but it should never be frosty.
• The outdoor coil can be cleaned with a garden hose.  Never use a pressure washer or brush on the coils, they will be damaged immediately. The condensing coils need to breathe, so keep plants and objects away 
• Keeps dogs away from the outside unit.  Their pee will corrode the aluminum fins very quickly and lead to a failed unit.
• Most importantly, replace the filter in your central air system.  If you have a mini-split heat pump, then you will clean or replace the filters on the inside units, as specified by the manufacturer.  Some Mitsubishi heat pumps come with a charcoal filter additionally to the main filter.  You should check these filters frequently to keep your system running well. You can also get anti-allergen filters for some brands, including Mitsubishi. 
• When everything is ready, you can turn the unit on at the outside disconnect, then you can turn on the thermostat, or the inside units, as the case may be.
• Don't forget to change the batteries in your thermostat, if they have one.  Thermostats behave strangely when the battery starts to get low, you may save yourself a service call that way.

Try these steps first.  If the system is not cooling, then call an experienced tech who can check refrigerant levels and troubleshoot further.  If you have an old R-22 unit, then its time to think about upgrading to a newer more efficient and environmentally friendly one.