No power, no start
When Your AC Won't Turn On
A system that doesn't respond at all is often a power or control issue, and a few simple checks can sometimes get it running again.
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Quick answer
An AC that won't turn on usually has a power or control problem: dead thermostat batteries, a wrong setting, a tripped breaker, a switched-off furnace or air handler, or a safety float switch tripped by a clogged drain. A failed capacitor, contactor or control board can also stop it. Check the thermostat, breaker and power switch first. If the system still won't start, call for service.
What may be going on
Likely causes
Thermostat issues
Dead batteries, a blank screen, or the mode set to Heat or Off will keep the AC from getting a call to cool.
Tripped breaker
A power surge, a struggling motor or a wiring fault can trip the AC breaker, cutting power to the indoor or outdoor unit.
Indoor power switch off
The furnace or air handler has a light-switch style power switch nearby that can get bumped off by accident.
Float switch tripped
When a blocked line fills the drain pan, a float switch cuts power to the system so water doesn't spill.
Failed electrical part
Several electrical parts, such as the capacitor, contactor, transformer or control board, can fail and leave the system dead.
Safe first checks
- Replace thermostat batteries and confirm it is set to Cool below room temperature.
- Check the main panel for a tripped AC or furnace breaker and reset it once.
- Make sure the power switch by the furnace or air handler is on.
- Without opening panels, look at the drain pan for standing water that could have tripped a float switch.
- Wait a few minutes after any reset; many systems have a built-in delay.
What not to do
- Don't reset a breaker more than once if it trips again.
- Don't bypass or disconnect a float switch to force the system on.
- Don't open the thermostat wiring or the outdoor electrical panel.
When to call
When to call a technician
If the thermostat has power, the breaker holds, and the switches are on, but nothing happens, an internal electrical part or control likely failed. A breaker that trips immediately after reset also points to a short or a failing component.
These issues involve high voltage and need proper testing. Calling the number on this page links homeowners with independent providers for AC repair, and if the thermostat itself seems at fault, thermostat service may help.
- Breaker trips again right after reset
- Thermostat has power but nothing starts
- Burning smell near the unit or panel
- Water in the drain pan with the system shut down
What a technician may inspect
- Low-voltage thermostat wiring and signals
- Transformer and control board output
- Capacitor and contactor condition
- Breaker, disconnect and wiring connections
- Float switch and condensate drain
Keeping it from happening again
Swap thermostat batteries once a year, keep the condensate drain clear, and have electrical parts checked during regular maintenance. Older systems may show worn contactors or brittle wiring that a technician can spot before a hot day.
Where to go next
Related service and market pages
Some systems have a short delay after power returns, and a surge can trip the breaker. Wait a few minutes, check the breaker, and reset it once if needed. If it still won't start, a part may have been damaged.
It can. Plenty of systems use a float switch that cuts power once the drain pan fills. Clearing the line requires care, so have a technician check it if you see standing water.
Not always. Dead batteries or a tripped breaker can blank the display. Replace batteries and check power first. If it stays blank, the thermostat or its wiring may need service.
Call now
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 your part of Kentucky or Southern Indiana.
CALL NOW[TRACKED_PHONE]For homeowners who need new HVAC or AC service: repair, replacement or installation. The line can't help with billing or existing-customer service.