The 115-Degree Week Playbook
When the Valley strings together a week of extreme heat, a few deliberate changes make a real difference.
During an extreme Phoenix heat wave, pre-cool the house in the morning, hold a steady thermostat setting rather than lowering it further, close all blinds before the sun reaches the glass, run ceiling fans in occupied rooms, shift heat-producing appliances to night, and rinse the condenser coil if it has been a while.
What changes at 115 and above
Air conditioning capacity falls as outdoor temperature rises, because the condenser has to reject heat into hotter air. At the same time, the load on your house climbs. Both curves move against you at once.
Equipment in the Valley is typically sized to a design temperature around 108 to 110 degrees. On days well above that, a correctly sized, healthy system running continuously and drifting a degree or two above setpoint is behaving exactly as designed.
That is not a failure. It is the arithmetic of the day, and understanding it prevents a lot of unnecessary worry — and a lot of unnecessary thermostat adjustment.
The playbook
- Pre-cool in the morning. Bring the house down a couple of degrees below your normal setting while outdoor temperatures are lower and the system has capacity to spare.
- Hold steady through the afternoon. Lowering the setpoint further does not increase capacity. It just guarantees continuous runtime with no possibility of satisfying.
- Close blinds before the sun reaches the glass, not after the room is already warm. West windows by noon.
- Run ceiling fans in occupied rooms only. Three to four degrees of perceived cooling for very little energy. Off when you leave.
- Shift heat-producing loads to night. Oven, cooktop, dryer, dishwasher.
- Keep exterior doors closed and minimize openings during peak hours.
- Check the filter and rinse the condenser coil if it has been a while.
- Flush the condensate drain. The system is producing maximum water.
Managing expectations by the numbers
| Outdoor temp | Realistic indoor expectation |
|---|---|
| Up to 105°F | A healthy system holds setpoint comfortably |
| 105–112°F | Holds setpoint, running long cycles or continuously |
| 112–118°F | May drift 1–3°F above setpoint in the late afternoon |
| 118°F+ | Drifting a few degrees is normal for correctly sized equipment |
If your house drifts eight or ten degrees on a 112-degree afternoon, that is a fault rather than physics. The heat wave exposed it; it did not cause it.
Rinsing the coil mid-heat-wave
This is one of the few interventions that produces an immediate, measurable improvement during a heat wave, and it takes fifteen minutes.
Kill power at the outdoor disconnect. Rinse the condenser coil gently with a garden hose, directing water from the inside of the coil outward where you can reach. Let it dry, restore power.
On a coil carrying a season of dust, that alone can restore meaningful capacity at exactly the moment you need it. Never use a pressure washer — it flattens the aluminum fins permanently.
When it stops being about comfort
If the system fails during a heat wave, the situation changes from an inconvenience to a safety matter faster than most people expect.
Above the mid-90s indoors, risk rises sharply for adults over 65, infants, people with cardiovascular or respiratory conditions, anyone on medications affecting thermoregulation, and pets.
Have a plan before you need it. Know where you would go — a relative, a hotel, a library, a cooling center. Dialing 2-1-1 connects you to current cooling center locations. And if the house is climbing with vulnerable people in it, leave rather than waiting for a truck.
What to expect from us during a heat wave
Every HVAC company in the Valley runs at capacity during a sustained heat wave. That is simply true, and companies claiming otherwise are managing expectations rather than describing reality.
We triage by severity: burning smells and electrical faults first, then active water intrusion, then no-cool situations with vulnerable residents or the highest indoor temperatures.
And we give honest arrival windows. If we cannot reach you today, we say so, so you can decide where to spend the night rather than waiting up for a truck that is not coming.
Frequently asked
Is it normal for my A/C to struggle at 115 degrees?
Drifting one to three degrees above setpoint in the late afternoon is normal for correctly sized equipment, because capacity falls as outdoor temperature rises while the load climbs. Drifting eight or ten degrees indicates a fault the heat wave exposed.
Should I lower my thermostat during a heat wave?
No. Lowering the setpoint does not increase the system's capacity — it just guarantees continuous runtime with no possibility of satisfying. Pre-cool in the morning while the system has capacity to spare, then hold steady.
What helps most during extreme heat in Phoenix?
Pre-cooling in the morning, closing blinds before the sun reaches the glass, running ceiling fans in occupied rooms, shifting heat-producing appliances to night, and rinsing a dusty condenser coil — which can restore real capacity in fifteen minutes.