The number one reason for service calls in the summertime: Dirty Filters!
Make sure that your filter is clean. Some homes require a filter change every month while others only need a new filter every 6 months. Many filters are too restrictive and cause great strain on residential heating and cooling systems. If you hear a whistling coming from your filter cabinet, or a struggling blower motor inside your furnace, consider using a less restrictive filter. Plugged/restrictive filters can also cause ice to form on the cooling coil above your furnace!
Do you program your thermostat to limit runtimes during the day or night? In extreme hot and humid temperatures, your air conditioner, even if sized properly, is not designed to cool and dehumidify your entire home quickly. It can take hours and sometimes days to cool down a hot and humid home. During the hot and sticky summer months, we encourage homeowners to keep the temperature in their homes as close to static as possible. Feel free to close (a few) vents in your basement to help force cooler air upstairs. Just be mindful to not close too many! Also, make sure that all of your return air grills (larger grills than supply) are unobstructed. Find the return air vents upstairs and make sure they are clear; in multi-story homes, these are the most important during the summer months.