AC Not Turning On? 10 Things to Check Before You Call

Quick answer: If your AC won't turn on, check the thermostat (set to Cool, below room temperature, fresh batteries), the breakers for both the indoor and outdoor units, the outdoor disconnect switch, and whether a clogged condensate drain has tripped the float switch. If the indoor fan runs but the outdoor unit stays silent, a failed capacitor or contactor is the usual culprit. If a breaker trips again after resetting, stop and call for AC repair.

A dead air conditioner on a hot New Jersey afternoon is miserable, but many no-start problems have simple causes. Work through these checks in order.

1. Thermostat mode and setting

Make sure the thermostat is set to Cool (not Heat, Off or Fan) and the setpoint is a few degrees below the room temperature. Smart thermostats can be stuck on a schedule, a vacation hold or an energy-saving event from your utility. See thermostat not working.

2. Thermostat batteries and display

A blank or dim display means dead batteries or no power. Replace batteries; if the thermostat is hard-wired and still blank, a tripped breaker or blown fuse at the air handler may be the cause.

3. Wait for the delay

Many systems have a built-in delay of a few minutes after being turned off or after a power outage, to protect the compressor. Give it five minutes.

4. Breakers

Central AC usually has two breakers: one for the indoor air handler or furnace and one (a double breaker) for the outdoor condenser. Check both. If one is tripped, reset it once. If it trips again, don't keep resetting it; that indicates an electrical fault, a failing compressor or a shorted motor.

5. The outdoor disconnect

Next to the outdoor unit there's a disconnect box with a pull-out block or a switch. It's easy for someone to bump or a landscaper to switch off. Make sure it's on.

6. The furnace or air handler switch

Your indoor unit has a service switch, often on the wall nearby, that looks like a light switch. If it's off, nothing runs. Also check that the furnace door panel is fully closed; many units have a safety switch that cuts power when the panel is off.

7. The condensate float switch

Air conditioners remove water from the air, which drains away through a condensate line. If the line clogs, water backs up and a float switch shuts the system off to prevent overflow. Look for water in the drain pan or a pump that isn't working. Clearing the drain often lets the AC restart. See AC leaking water inside.

8. A dirty filter or frozen coil

A badly clogged filter can freeze the indoor coil; some systems then shut down on a safety. Replace the filter and let the ice melt before restarting (run the fan only for a few hours). See why your AC is freezing up.

9. Indoor fan runs, outdoor unit doesn't

If air blows but it isn't cold and the outdoor unit is silent (or humming without spinning):

• Failed capacitor: the most common cause. Capacitors help start the compressor and fan motor and often fail in summer heat.
• Bad contactor: the switch that powers the outdoor unit can burn or stick.
• Low-voltage wiring: chewed or damaged thermostat wiring between the units.

Turn the system off so the indoor coil doesn't freeze, and call for service. Capacitors store a dangerous charge; don't try to replace them yourself.

10. Outdoor unit runs but no cold air

If both units run but the air isn't cool, see AC running but not cooling. Low refrigerant, a dirty outdoor coil or a failing compressor are common causes.

Preventing no-start problems

• Schedule a spring AC tune-up: it tests capacitors and contactors and clears drains before they fail
• Change filters regularly
• Keep the outdoor unit clear and clean (rinse salt off coils at the shore; see salt air corrosion)
• Have the condensate drain treated or flushed each season

When it's an emergency

If it's dangerously hot, especially for older family members, infants or anyone with health conditions, treat it as urgent and call our 24/7 emergency line.

What a technician checks on a no-start call

When we arrive for an AC that won't start, we work through the system methodically: confirming the thermostat is calling for cooling, checking low-voltage wiring and fuses on the control board, testing the capacitor and contactor, checking the float switch and drain, measuring voltage at the outdoor unit, and checking the compressor and fan motor. Once the cause is found, we explain it and give you an upfront price before any repair.

After a power outage or storm

If your AC stopped after a power outage, thunderstorm or brownout, check the breakers and give the system a few minutes before restarting. Power surges can damage capacitors, control boards and compressors. If the system still won't run, or you smell burning or hear buzzing, turn it off at the thermostat and call for service rather than repeatedly trying to restart it.

Same day AC repair

We repair all brands of air conditioners across Ocean, Monmouth, Burlington and Middlesex counties, including AC repair in Toms River, Freehold Borough, Piscataway and Maple Shade. Book online or call for same day service and an upfront price.