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Air conditioning failure during extreme heat

When an central air conditioner or HVAC system breaks down during severe summer heatwaves or dangerous high-humidity weather, indoor temperatures can rise rapidly to dangerous levels, posing severe health risks for infants, older adults, and pets.

Do this now

  1. Check your main electrical breaker panel to see if the AC circuit breaker tripped. Reset it once if tripped.
  2. Verify that your thermostat is set to Cool and the target temperature is set below current room temperature.
  3. Replace dirty or clogged HVAC air filters immediately, as blocked air filters cause cooling coils to freeze over.
  4. Close all blinds, drapes, and curtains on sunny windows to block direct radiant heat.
  5. Move vulnerable family members, older adults, and pets to the lowest floor, basement, or a shaded interior room.

Passive home cooling strategies

If repair technicians cannot arrive immediately, keep indoor temperatures manageable:

  • Create cross-ventilation at night: If outdoor night temperatures drop below indoor room temperatures, open windows on opposite sides of the home and use box fans to pull cool air in.
  • Block daytime heat: Keep all windows, doors, and blinds closed tight during peak daytime heat hours (10:00 AM to 6:00 PM).
  • Use ceiling fans correctly: Ensure ceiling fans rotate counter-clockwise at high speed to create a cooling wind-chill effect.
  • Avoid heat-generating appliances: Do not use stoves, ovens, dishwashers, or clothes dryers during hot hours. Eat cold meals or use outdoor grills.

Personal cooling and heat illness prevention

Keep human bodies cool even when indoor air is warm:

  • Hydrate continuously: Drink cool water continuously throughout the day, even if you do not feel thirsty. Avoid alcohol, caffeine, and high-sugar drinks.
  • Cool water therapy: Take cool showers or baths, apply damp cool towels to neck, armpits, and wrists, or use misting spray bottles.
  • Seek temporary cooling centers: Spend peak afternoon hours in air-conditioned public spaces (libraries, shopping malls, community cooling shelters, movie theaters).

Basic AC troubleshooting steps

Before calling an emergency HVAC technician:

  • Check outdoor unit: Ensure the outdoor condenser fan unit is free of leaves, tall grass, or debris, and verify that the outdoor power shutoff switch is on.
  • Thaw frozen coils: If ice has built up on refrigerant lines or indoor coils, turn the thermostat system setting to Off and turn the fan setting to On to allow ice to melt completely over 2 to 4 hours before restarting.
  • Clear condensate drain line: Clean clogged condensate drain lines if the unit shut off due to a full drain pan safety float switch.