How to avoid your air-conditioning conking out on the hottest day of the summer:
Have a professional check your system periodically.
Oil the blower motor and fan on both the condensing and the evaporation units annually.
Keep the condensing-unit pan free of bugs, leaves and dirt.
Check the tension on the condensing and evaporation unit blower fan belts each spring.
Inspect the blower ducts and joints for leaks and insulation slippage annually.
Clean or replace air filters frequently - a home without pets: every 90 days. One dog or cat: every 60 days. More than one pet or if anyone has allergies: 20–45 days
Keep the blower motor fan blade free of mold and mildew.
Set your a/c fan speed on high except when it’s humid.
Use a whole-house attic fan.
Set your thermostat as high as comfortably possible in the summer.
Don't place electronic equipment near your air-conditioning thermostat.