AC not turning on: the five-minute checklist

Work through these in order

• Thermostat batteries. A dead battery in a battery-powered thermostat looks exactly like a dead air conditioner. Replace them first, every time.
• Thermostat mode and setpoint. COOL selected, and set at least three degrees below the current room reading. Some systems will not call for cooling on a smaller gap.
• The breaker panel. Look for a breaker sitting between ON and OFF. Push it fully OFF, then firmly back ON. If it trips again immediately, stop and call. A repeatedly tripping breaker is a fault, not an inconvenience.
• The outdoor disconnect. There is a small box near the outdoor unit with a pull-out handle. It can be knocked loose by landscaping work. Make sure it is seated fully.
• The condensate float switch. On attic and closet systems, a clogged drain fills a pan and trips a switch that shuts cooling off on purpose, to stop water coming through your ceiling. If the pan has water in it, this is your answer.
• The filter. A filter so clogged it froze the coil will shut the system down. If you see ice, turn the system off, set the fan to ON to thaw it, and replace the filter.
• The indoor unit switch. Many air handlers have a light-switch style shutoff nearby that gets flipped by mistake, often by someone looking for the attic light.
• Anything else. If all eight check out, the fault is electrical or mechanical, and it needs someone with a meter.

What each outcome usually means

When to skip the checklist entirely

If you smell burning, if a breaker trips more than once, or if it is above 95 outside with an infant, an elderly resident, or someone with a medical condition in the house, do not work through a list. Call, and say who is in the house.

There is no charge for asking, and no overtime charge for the hour you happen to be asking at.