Emergency HVAC Failure During Extreme Heat Checklist

Heat rises, so ground-floor or basement rooms are 5–10°F cooler than upper levels. Close blinds and curtains on sun-facing windows. Children under 4, adults over 65, and anyone on medications that impair sweating are at highest risk for heat exhaustion.

Place one fan blowing inward on the shaded side of the house and another blowing outward on the sun side. This creates airflow that can drop perceived temperature by 5–8°F. If outdoor temperature exceeds indoor temperature, keep windows closed — fans just blow hotter air in.

Dehydration accelerates heat illness. Adults need 8–12 oz of water every 20 minutes in extreme heat without AC. Watch for signs of heat exhaustion: heavy sweating, nausea, dizziness, rapid pulse. If someone stops sweating or becomes confused, call 911 — that's heat stroke.

Dogs and cats overheat faster than humans. Move them to the coolest room, provide fresh cool water, and place damp towels on tile floors for them to lie on. Signs of pet heat distress include excessive panting, drooling, lethargy, and vomiting.

It sounds obvious, but accidental setting changes cause a surprising number of emergency calls. Verify the display is on, batteries aren't dead (if battery-powered), and the fan is set to AUTO, not OFF. Try lowering the set point 5°F below the current reading.

HVAC systems typically have two breakers — one for the indoor air handler and one for the outdoor condenser. A tripped breaker sits in the middle position between ON and OFF. Flip it fully OFF, wait 30 seconds, then flip back ON. If it trips again immediately, do not reset it again — that indicates a short circuit that needs a technician.

A severely clogged filter restricts airflow enough to freeze the evaporator coil, which shuts down cooling entirely. Pull the filter out and hold it up to light — if you can't see through it, it's overdue. Replace with any filter that fits. During extreme heat, a clean filter is more important than a high-MERV rating.

A frozen coil means the system is running but not cooling. Turn the system to FAN ONLY (not off) for 1–2 hours to thaw the coil, then restart in COOL mode. If it freezes again, you likely have a refrigerant leak or blower motor issue — call a technician.

Go outside and check whether the outdoor unit's fan is spinning. If not, check for a local disconnect switch on the wall near the unit — it may have been turned off. Clear any debris, leaves, or objects within 2 feet of the unit that could block airflow. A condenser that can't exhaust heat can't cool your home.

The first company you call may be booked 2–3 days out. Call multiple contractors simultaneously. Clearly state that you have no cooling during extreme heat and mention if vulnerable people (elderly, infants) are in the home — many companies prioritize medical-risk households.

Emergency and after-hours HVAC calls typically add $100–$300 on top of the diagnostic fee. Ask what the total minimum charge is before they arrive. Most companies charge $75–$150 for the diagnostic visit, plus parts and labor for the repair.

Technicians triage calls based on symptoms. Telling them 'my 12-year-old Carrier unit is running but blowing warm air' is far more useful than 'my AC is broken.' Check the outdoor unit for a model number sticker — the first two digits of the serial number are often the manufacture year.

A 10,000–14,000 BTU portable AC unit ($300–$500 at hardware stores) can cool one room adequately. During heat emergencies, concentrate cooling in one room rather than trying to cool the whole house. This is also a good permanent backup for future failures.

A spring tune-up ($100–$200) catches low refrigerant, weak capacitors, and worn contactors before they fail during the first heat wave. The technician checks charge levels, cleans coils, tests electrical connections, and verifies thermostat calibration.

Dirty filters are the #1 preventable cause of HVAC failure. During heavy summer use, filters clog faster than you think. Set a calendar reminder. A $10 filter every 60 days prevents a $500 frozen-coil service call.

Plants, mulch, and stored items reduce condenser airflow and force the system to work harder. Clear the area seasonally and never stack anything against the unit.