Why Heat Waves Are Hard on Your AC
When the DFW forecast shows a string of 100-plus degree days, your air conditioner is working against a much bigger temperature gap than usual. A system that comfortably holds 74 degrees on an 85-degree day has to run far longer, and often more frequently, to hold that same temperature when it's 105 outside. Most residential systems are sized for typical summer peaks, not extended heat waves, so during these stretches your equipment runs close to its maximum capacity for hours at a time.
That extended run time isn't necessarily dangerous for a well-maintained system, but it does expose weak points. A slightly low refrigerant charge, a dirty condenser coil, or a clogged filter that barely mattered in April can turn into a real performance problem in August. Understanding how heat waves stress your air conditioning system is the first step to keeping your home comfortable without an emergency repair call in the middle of the worst heat.
Smart Thermostat Settings That Help
One of the most effective things you can do during a heat wave is stop asking your AC to make dramatic temperature swings. Every degree you ask the system to drop quickly, especially from a hot afternoon peak, adds strain and run time.
- Set your thermostat to a temperature you can hold steady all day rather than lowering it drastically when you get home.
- Use a modest 4-6 degree setback while away instead of a wider swing; a bigger drop takes much longer to recover on a 105-degree day.
- If you have a smart thermostat, take advantage of scheduling features to pre-cool the home slightly before the afternoon peak rather than fighting the heat head-on at 4 p.m.
- Avoid the temptation to set the thermostat far colder than you actually need "to cool faster." Most systems cool at a fixed rate regardless of the target temperature, so this only makes the unit run longer.
Small, steady adjustments let your system work efficiently instead of chasing large temperature swings during the hottest part of the day.
Reduce the Heat Load Inside Your Home
Your AC isn't just fighting outdoor heat — it's fighting every heat source inside your home too. During a heat wave, small changes in daily habits can meaningfully reduce how hard your system has to work.
- Close blinds and curtains on south- and west-facing windows during peak sun hours; direct sunlight through glass adds a surprising amount of heat load.
- Run ovens, dryers, and dishwashers in the early morning or late evening instead of midday.
- Use ceiling fans to create a wind-chill effect so you're comfortable at a slightly higher thermostat setting — just remember to turn them off in empty rooms since fans cool people, not spaces.
- Check that supply and return vents aren't blocked by furniture or rugs, which can restrict airflow through your ductwork and make rooms feel warmer than the thermostat suggests.
- Change your air filter if it's been more than 60-90 days; a clogged filter restricts airflow and forces the system to run longer to move the same amount of cool air.
These habits won't replace a properly sized system, but they take real pressure off your AC during the hottest stretches of summer.
Give Your Outdoor Unit Room to Breathe
The outdoor condenser unit has to reject a large amount of heat during a heat wave, and anything that restricts its airflow makes that job harder. Walk outside and check that there's at least two feet of clearance around the unit — grass clippings, fallen leaves, mulch, and overgrown shrubs all reduce airflow across the coil.
It also helps to rinse the outdoor coil gently with a garden hose (power off) if you notice visible dirt or cottonwood fluff built up on the fins, which is common in North Texas neighborhoods with mature trees. Avoid running the unit in direct, unshaded areas if you can help it during installation planning, though for existing units this isn't something to change mid-summer — just keep the area clear and clean.
If your unit sits in an area that gets intense afternoon sun with no airflow relief, that's worth mentioning at your next maintenance visit so a technician can evaluate whether it's affecting performance.
What We See on 105-Degree Days in DFW
Spencer technicians have been running service calls across Irving and the Metroplex since 1960, and heat waves follow a predictable pattern every year. The calls that spike hardest aren't usually total system failures — they're systems that were already borderline and finally got pushed over the edge by extreme heat. A slightly undercharged system that cooled "well enough" in May suddenly can't keep up when it's 106 outside. A dirty coil that cost a home a couple of degrees of efficiency in spring costs it five or six degrees during a heat wave.
We also see a steady rise in short-cycling complaints during heat waves — units turning on and off rapidly instead of running a full cooling cycle. This is often tied to airflow restrictions or a thermostat location that's picking up heat from a nearby appliance or sunny window, giving a false reading. Homeowners who scheduled a spring tune-up almost always weather these stretches better than those who haven't had the system checked in over a year, simply because small issues get caught before the heat exposes them.
Warning Signs You Shouldn't Ignore
During a heat wave, don't wait to call if you notice any of the following:
- The system runs constantly but the house never quite reaches the set temperature.
- Warm air blowing from vents that were previously cold.
- Ice forming on the indoor coil or refrigerant lines.
- A noticeable increase in humidity indoors even with the AC running.
- Unusual noises — grinding, squealing, or a hard clunk on startup.
Any of these can indicate the system is losing the fight against the heat, and pushing it further without a repair risks a full breakdown on the hottest day of the year. If you're already noticing strain, it's worth reviewing our FAQ page or having a technician take a look before the next heat wave arrives.
Why Humidity Makes Heat Waves Feel Worse
A 100-degree day in DFW rarely feels like a dry 100 degrees. North Texas summers typically carry relative humidity in the 40-60% range even during the hottest stretches, and that moisture changes how your AC has to work and how hot the house actually feels. Your air conditioner does two jobs at once: it lowers the air temperature and it pulls moisture out of the air as that air passes over the evaporator coil. During a heat wave, the system is asked to do both jobs at a much larger scale, which is part of why run times stretch so long.
Humidity also affects comfort independent of the thermostat reading. A home sitting at 74 degrees with 65% relative humidity feels noticeably stickier and warmer than the same 74 degrees at 45% humidity, because your body cools itself primarily through evaporating sweat, and that process slows down when the surrounding air is already saturated with moisture. This is why some homeowners keep bumping the thermostat down during a heat wave without actually feeling more comfortable — the real culprit is humidity, not temperature.
A well-maintained system with correct refrigerant charge and clean coils removes humidity efficiently as a byproduct of normal cooling. A system that is short-cycling, oversized for the space, or running with reduced airflow often cools the air quickly without running long enough to pull much moisture out, leaving a home that reads cool on the thermostat but still feels clammy. If your home consistently feels muggy during heat waves even when the temperature seems under control, mention it at your next maintenance visit — it may point toward a duct, sizing, or runtime issue rather than anything wrong with the thermostat setting itself. In some cases, a dedicated dehumidification accessory paired with your existing system can address this more directly than adjusting the thermostat alone.
Get Ahead of the Next Heat Wave
DFW summers aren't getting any milder, and the systems that handle heat waves best are the ones that go into summer already tuned up. If your AC is struggling to keep pace with triple-digit days, or you just want peace of mind before the next stretch of extreme heat, our Comfort Maintenance Plan starting at $199 a year includes the seasonal check-ups that catch small problems early.
Call Spencer Air Conditioning & Heating at 972-446-2665 to schedule service or ask questions about keeping your home comfortable through a Texas heat wave.
Spencer Air Conditioning & Heating — Serving DFW Since 1960. License TACLA115636C