Quick Answer
If your AC won't turn on, check these first: (1) Thermostat settings and batteries, (2) Circuit breakers for both indoor and outdoor units, (3) The emergency shutoff switch, (4) Your air filter—a clogged filter can trigger safety shutoffs. If those all check out, the issue is likely a failed capacitor, contactor, or control board—which require professional repair. In Charlotte's summer heat, a non-working AC is an emergency. Same-day service is available.
When your AC won't turn on, it's easy to assume the worst. But before you panic, know this: about half of "AC not turning on" service calls are caused by simple issues you can fix yourself in minutes. Let's walk through what to check before calling for repair.
1. Check Your Thermostat
This sounds obvious, but thermostat issues cause more "AC won't start" calls than you'd think.
Thermostat Checklist
- Is it set to COOL (not HEAT or OFF)?
- Is the set temperature LOWER than the current room temperature?
- Is the fan set to AUTO or ON?
- Are the batteries dead? (Replace them even if the screen is on)
- Is the display completely blank? Check breaker.
Pro Tip
2. Check Circuit Breakers
Your AC system has TWO circuits—one for the indoor unit (air handler/furnace) and one for the outdoor unit (condenser). Both must be on for the system to work.
Checking Breakers
- 1
Find your electrical panel
Usually in the garage, basement, or utility room.
- 2
Look for breakers labeled HVAC, AC, Air Handler, or Furnace
You may have 2-3 breakers related to your system.
- 3
Check for tripped breakers
A tripped breaker sits in the middle position, not fully ON or OFF.
- 4
Reset by flipping fully OFF, then ON
If it trips again immediately, stop—you have an electrical problem that needs professional diagnosis.
Important
3. Check the Emergency Shutoff Switch
Most HVAC systems have an emergency shutoff switch that looks like a light switch, usually located near the indoor unit or at the top of basement stairs. It's often accidentally turned off.
Look for a switch on or near your furnace/air handler. It may be in a small red plate or labeled "Emergency" or "HVAC." Flip it on if it's off.
4. Check Your Air Filter
A severely clogged air filter restricts airflow, causing the system to overheat. Many systems have a safety switch that shuts down the unit when this happens.
Pull out your filter and check it. If you can't see light through it, it's clogged. Replace it, then try starting the system again. The system may need 30 minutes to reset after overheating.
5. Check the Outdoor Unit Disconnect
There's a disconnect box on the wall near your outdoor AC unit. Inside is either a pull-out block or a breaker. Make sure it's in the ON position and fully seated.
While you're outside, look at the condenser unit itself. Is the fan spinning when the system should be running? If the fan isn't spinning but you hear humming, the capacitor may have failed.
6. Check the Condensate Drain Pan
Your AC removes humidity, and that water drains into a pan and out through a drain line. If the drain is clogged, the pan fills up and triggers a float switch that shuts down the system to prevent water damage.
Look for water in the drain pan under your indoor unit. If it's full, the drain line is clogged. You can try clearing it with a wet/dry vacuum on the drain line outlet (usually outside), but this often requires professional cleaning.
7. Wait After a Power Outage
If your AC stopped working after a power outage or surge, the system may need time to reset. Modern systems have protection circuits that prevent immediate restart.
Turn the thermostat off, wait 5 minutes, then turn it back to cool. If it still won't start, try resetting the breakers.
8. Listen for Clues
What you hear (or don't hear) tells you a lot:
| What You Hear | Likely Cause | DIY or Pro? |
|---|---|---|
| Nothing at all | Power issue (breaker, switch, thermostat) | Check DIY items above |
| Click from thermostat, nothing else | Control board, contactor, or wiring issue | Call for service |
| Humming from outdoor unit, fan not spinning | Failed capacitor or fan motor | Call for service |
| Buzzing or chattering | Contactor failing | Call for service |
| Indoor fan runs, outdoor unit dead | Outdoor unit power or control issue | Check outdoor breaker, then call |
When to Call a Professional
If you've checked all the items above and your AC still won't turn on, the problem is likely:
- Failed capacitor (most common repair we see)
- Bad contactor
- Faulty control board
- Wiring issue
- Failed compressor (less common, more expensive)
These all require professional diagnosis and repair. If you're in <a href="/services/ac-repair/indian-trail">Indian Trail</a>, <a href="/services/ac-repair/monroe">Monroe</a>, <a href="/services/ac-repair/matthews">Matthews</a>, <a href="/services/ac-repair/mint-hill">Mint Hill</a>, or surrounding Charlotte areas, we offer same-day <a href="/services/emergency-hvac-repair">emergency AC repair</a> service.
AC Repair Costs
Common "AC Won't Turn On" Repairs
| Service | Cost | Notes |
|---|---|---|
| Capacitor replacement | $150-$300 | Most common fix |
| Contactor replacement | $150-$350 | Common wear item |
| Control board replacement | $400-$700 | Less common |
| Fan motor replacement | $300-$600 | If motor has failed |
| Compressor replacement | $1,500-$2,500 | Major repair, consider system age |
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Written by
Kodiak HVAC Team
HVAC professional at Kodiak Heating & Cooling.