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What to do when the AC quits in 115 degree heat

Request service, check the breakers and filter, and move anyone at risk to an air-conditioned place. Don't count on the night to cool the house. Sky Harbor recorded 29 nights in 2026 that never dropped below 90°F.

Updated October 28, 2026 · Sources listed at the end

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On this page
  1. Check these first
  2. Keep people safe
  3. Slow the heat gain while you wait
  4. How hot it gets

Check these first

  1. Thermostat: set to cool, below room temperature, batteries good, screen on. If "cool on" is flashing, wait five minutes; it may be the compressor delay.
  2. Breakers: the air handler and the outdoor unit usually have separate breakers. Reset a tripped one once. If it trips again, leave it off.
  3. Filter: if it's clogged, replace it.
  4. Ice on the copper lines or the indoor coil: set the system to off and the fan to on so it thaws. Running a frozen system can damage the compressor.
  5. Outdoor unit: is the fan turning? Is it humming without running? Either way, turn the system off at the thermostat and wait for the technician.

Don't open the outdoor unit's electrical panel or poke the fan to get it spinning. Capacitors hold a dangerous charge.

Keep people safe

Maricopa County's 2025 heat deaths report found that in indoor heat deaths where an air conditioner was present, it wasn't working 72% of the time. The National Weather Service lists these signs of heat exhaustion:

  • heavy sweating
  • weakness or tiredness
  • cool, pale, clammy skin
  • a fast, weak pulse
  • muscle cramps
  • dizziness, nausea or vomiting
  • headache
  • fainting

Move the person somewhere cooler, air-conditioned if possible. Get medical help if they vomit or symptoms last more than an hour.

A body temperature above 103°F with hot, red skin can be heat stroke. Call 911. The NWS says not to give fluids to someone with heat stroke.

  • The CDC says fans won't prevent heat illness when it's really hot, and even a few hours in air conditioning helps.
  • The NWS says not to point a fan at yourself when the room is above 90°F, and to check on older and frail neighbors.
  • Dial 2-1-1 for cooling locations and heat relief transportation. The county's Heat Relief Network map is at hrn.azmag.gov.
  • The City of Mesa loans free portable AC units to vulnerable residents without working AC: 480-644-6454.

Slow the heat gain while you wait

  • Close blinds and curtains, especially on west and south windows.
  • Shut doors to rooms you aren't using and stay in the coolest one.
  • Skip the oven and the dryer.

How hot it gets

Through October 24, 2026, 2026 had 39 days at 110°F or more at Sky Harbor and a high of 117°F on July 24, 2026. The record there is 122°F, set June 26, 1990. A closed house without cooling heats up all afternoon and holds it overnight, so plan to leave rather than wait it out.

Average daily high and low by month, Phoenix Sky Harbor

100°80°January: average high 67.5°F, average low 45.4°F6845JanFebruary: average high 72.2°F, average low 48.8°F7249FebMarch: average high 78.1°F, average low 54.5°F7855MarApril: average high 88.2°F, average low 62.1°F8862AprMay: average high 95.3°F, average low 69.8°F9570MayJune: average high 106.3°F, average low 80.6°F10681JunJuly: average high 108.6°F, average low 86.5°F10987JulAugust: average high 106.7°F, average low 84.8°F10785AugSeptember: average high 101.6°F, average low 79°F10279SepOctober: average high 91°F, average low 66.7°F9167OctNovember: average high 78.7°F, average low 55.2°F7955NovDecember: average high 69.4°F, average low 47.6°F6948Dec
Top number is the average high, bottom is the average low, 2016-2025. Source: NOAA NCEI daily summaries, station USW00023183.

Questions Mesa homeowners ask

Should I turn off my AC if it's not cooling?

If there's ice on the lines or coil, yes: set it to off with the fan on so it thaws. If the outdoor unit hums but won't start, turn it off and call. Running it can make the damage worse.

Can I call 911 if my AC is broken?

Call 911 for a medical emergency, such as signs of heat stroke. For the broken system, call an HVAC company. For a cool place to go, dial 2-1-1.

Keep reading

Serving East Mesa, Red Mountain, Las Sendas, Dobson Ranch, Eastmark, Gilbert, Chandler, Queen Creek, Apache Junction, Gold Canyon and all of Mesa.

Sources

  1. Maricopa County Department of Public Health: 2025 Heat-Related Deaths Report (April 2026)
  2. National Weather Service: Heat Cramps, Exhaustion, Stroke
  3. National Weather Service: During a Heat Wave
  4. CDC: Heat and People without Air Conditioning (June 25, 2024)
  5. City of Mesa: Heat Safety (accessed October 28, 2026)
  6. Maricopa Association of Governments: Heat Relief Network map
  7. Honeywell RTH2300 thermostat user manual: built-in compressor protection
  8. NOAA NCEI daily summaries, Phoenix Sky Harbor International Airport (USW00023183)