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No power, no start

AC Won't Turn On at All

A system that does nothing when the thermostat calls for cooling is frustrating, but it is often the easiest kind of problem to narrow down.

Quick answer

When an air conditioner will not turn on, the first suspects are simple: dead thermostat batteries, the wrong thermostat mode, a tripped breaker, a service switch turned off, or a full condensate pan that triggered a safety shutoff. If those check out, a failed capacitor, contactor, control board or compressor may be the reason, and that requires a technician.

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Hand adjusting a smart thermostat set to 72 degrees on a living room wall

What this symptom may mean

A completely silent system tells a different story than one that runs poorly. Either power is not reaching the equipment, the thermostat is not sending a signal, or a safety device has shut things down on purpose.

Work from the thermostat outward. Plenty of no-start calls end with fresh batteries or a flipped switch. If the basics are fine, the next steps belong to a professional.

Possible causes

  1. Thermostat batteries or settings

    A blank screen, a schedule override or a mode change can stop the call for cooling before it reaches the equipment.

  2. Tripped breaker

    Storms, surges or a failing part can trip the AC or air handler breaker.

  3. Service switch turned off

    Indoor units often have a switch nearby that looks just like an ordinary light switch.

  4. Condensate safety shutoff

    A float switch in a full drain pan cuts power to protect the home from water damage.

  5. Failed electrical component

    A bad capacitor, contactor, transformer or control board can leave the system unable to start.

Safe checks you can make

  • Replace thermostat batteries, then confirm the mode is COOL and the setpoint is below room temperature.
  • Check the main panel for tripped breakers labeled AC, condenser, furnace or air handler, and reset a tripped one once.
  • Find the service switch near the indoor unit and make sure it is on.
  • Look at the condensate line and any visible pan for standing water that may have triggered a shutoff.

What not to do

  • Don't reset a tripping breaker more than once. It is protecting the wiring from a real fault.
  • Don't open the electrical panel cover or the outdoor unit's service panel to look for loose wires.
  • Don't touch or try to test a capacitor.
  • Don't jump wires at the thermostat to force the system on.

When professional evaluation may be appropriate

If the thermostat has power, breakers and switches are on, the pan is dry, and the system still will not start, it is time to call. A technician can trace power through the system with proper meters and safety gear.

Call to be connected with a local provider for outdoor unit repair or general AC repair. If the thermostat itself seems at fault, see thermostat service.

  • The breaker trips again right after a reset
  • The thermostat works but the equipment never responds
  • A burning smell or scorch marks near the equipment

What an HVAC provider may inspect

  • Line and low voltage at each component
  • Transformer, fuses and control board
  • Capacitor and contactor
  • Compressor windings and start circuit

Keeping it from happening again

Swap thermostat batteries once a year, label the AC breakers clearly, and keep the drain line flowing. Spring and summer thunderstorms are common in central Alabama, so ask a provider to look over electrical parts after a season with frequent outages.

Where to go next

Related serviceAC Compressor & Condenser Repair

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Still not sure what's wrong?

Call and describe what you're seeing. You'll be connected with an independent HVAC provider serving homes in the Montgomery, AL area.

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The line is for homeowners who need HVAC or AC repair, replacement or installation. It can't help with billing or service already scheduled with a company.

Questions homeowners ask

AC Not Turning On: questions homeowners ask

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What does a dark, blank thermostat display tell me?

A blank screen usually means dead batteries, a tripped breaker on the air handler or furnace, or a safety switch that cut power. Some thermostats draw power from the equipment, so a tripped float switch can darken the screen too. Check batteries and breakers first.

Where is the service switch for my indoor unit?

It usually looks like a regular light switch on the wall or framing near the furnace or air handler, often in a closet, garage or attic. People sometimes flip it off by mistake. Turning it back on is safe, as long as you do not open any covers.

How long should I wait after resetting the breaker?

Many systems have a built-in delay of several minutes before the compressor restarts, which protects it. Give the system five to ten minutes after a reset. If it still does not start, or the breaker trips again, stop and call for diagnosis.

Can a power outage keep my AC from turning back on?

Yes. After an outage, some thermostats lose their settings, breakers can trip from the surge when power returns, and control boards can be damaged. Check the thermostat and breakers. If the system stays dead, a technician can test the electrical parts.

Is a dead AC usually a small fix or a major one?

It can be either. Many no-start problems come down to batteries, switches or a failed small electrical part. Others involve a control board or compressor. A provider can diagnose the cause and explain the options before any repair begins.

My outdoor unit runs but the inside is silent. What now?

That points to the indoor side: the blower motor, its capacitor, the control board, or a tripped indoor breaker or switch. Turn cooling off so the outdoor unit does not run without airflow, check the indoor breaker and switch, then call.