The correct time to schedule pre-season air conditioning maintenance is during late spring when warm summer weather is approaching. Maintenance includes cleaning the drip pan below the unit in the attic, flushing the drain pipe to the outside of the house, cleaning evaporator coils and debris from evaporator and condenser unit located outdoors, and finally following a few steps to see that your air conditioner is working correctly.
Turn your air conditioner on at the start of a warm sunny day. Set the thermostat to 65 degrees and check the inside ambient air temperature reading on the thermostat.
Place a thermometer against the inward-blowing air conditioner vent. Wait 15 minutes. Compare the temperature being emitted by the air conditioner against the ambient air temperature reading. The difference should be approximately 20 degrees Fahrenheit. If this isn't the case and the ambient temperature has gone up, call your HVAC contractor.
Remove the inspection cover from the base of the unit mounted in the attic with a screwdriver. If the drain pan is full and not draining properly, it may cause ice to form. Check to see if there is ice on the cold coil leading to the drain pan. If so, turn the air conditioner off and wait for the ice to melt.
Clean out the drain pan and clear the blockage. Go outside and locate the drain hose coming out the side of the house somewhere near the outside condenser unit. Wrap a rag around the outside of the pipe to act as a gasket. Place a wet-or-dry shop vacuum hose over the end. Turn the vacuum on and suck out the debris blocking the pipe.
Step indoors and turn the air conditioner back on. Wait 15 minutes and recheck the temperature difference between incoming air and ambient room temperature. If the problem persists, but the room seems to have cooled down somewhat, step outside. If the outside air is noticeably warmer, you may need to replace a faulty thermostat.
Go to the side of the house while the air conditioner is running. Check if the fan on top of the condenser unit is working. Don't poke anything into the fan; you will hear the fan running and feel air moving when holding your hand above the unit. If the fan is not working, the motor may be faulty out or your air conditioner compressor may have burned out. If the fan is working, the unit's outward facing cooling vanes surrounding the unit may be clogged.
Turn off the power at the junction box near the outside condenser unit if the fan is working. Clean out loose leaves, twigs, and debris collected between the cooling vanes on the outside of the unit. Attach a high-pressure spray nozzle to your garden hose. Direct a spray of water downward around the condenser unit to wash out collected debris. Restore power and carry out the indoor temperature checks once more.
Call your HVAC technician if the above steps don't correct the problem; there may be a faulty component, or your air conditioner may be leaking refrigerant and need recharging.