Heating and air · checked 5 Oct 2026
The AC won't turn on
Safety first
- If smoke appears, leave; call 911 from outside.
- If indoors gets hot, move vulnerable people somewhere air-conditioned.
- Keep equipment covers closed; never bypass safety switches.
Fix it nowEight steps
- Replace thermostat batteries only through its designated battery compartment, if equipped.Dead batteries can prevent cooling calls. Don't touch wiring.
- Set thermostat to COOL, fan AUTO, and temperature below room temperature.The thermostat must request cooling.
- Allow the thermostat's startup delay to finish; don't repeatedly change settings.A protective delay can temporarily prevent startup.
The other five steps
- Turn thermostat OFF before replacing a clogged, readily accessible filter.Use the same size and airflow direction; avoid equipment cabinets.
- Visually check labeled HVAC breakers; leave tripped breakers off for an HVAC technician.A trip can indicate an electrical fault. Never remove panel covers.
- Look for visible drain-pan water or ice without opening equipment or entering attics.Water or ice means stop; don't bypass the safety switch.
- If no warning signs exist, select COOL again; allow the startup delay.Check whether the safe adjustments restored operation.
- If still off, set thermostat OFF and call an HVAC technician.Internal electrical, drain, and refrigerant repairs require professional service.
When to stop
Stop and get a heating and air technician if:
- Smoke or flames: leave immediately; call 911 from outside.
- Burning odor, buzzing, or a tripped breaker: stop; call an HVAC technician. Don't reset repeatedly.
- Visible ice, standing drain-pan water, or water near electrical equipment: stop; call an HVAC technician.
- The AC remains off after these checks: stop troubleshooting; call an HVAC technician.
- Someone becomes confused, collapses, or has seizures in the heat: call 911; cool them with wet cloths while waiting.
What it probably is
Thermostat settings or dead batteriesDisplay is blank, shows low battery, or isn't set below room temperature.You can check
Interrupted electrical powerOther appliances are off, or a labeled HVAC breaker appears tripped.For a pro
Clogged air filterFilter is heavily clogged; restricted airflow can cause freezing or shutdown.You can check
Blocked condensate drainVisible water in the drain pan may have triggered the safety switch.For a pro
Failed electrical componentIndoor fan runs but outdoor unit stays off; humming may occur.For a pro
Time and parts
- Time
- About 10–15 minutes for basic checks, plus any thermostat startup delay.
- Parts
- $0–$30 estimated for batteries or a standard disposable filter; specialty filters cost more.
Get it done
More than a quick fix? Vora gets quotes privately and recommends one heating and air technician.
Checked against
- Carrier: AC Unit Not Turning On
- Trane: Thermostat Blinking Cool On
- CDC: Heat-related Illnesses
- US Fire Administration: Choosing and Using Fire Extinguishers
Written for Vora from these public sources and checked on 5 Oct 2026. General guidance, not a substitute for a pro on site. In danger, leave and call 911.