Your AC just stopped working. It's July. It's hot. Before you panic-call a tech at emergency rates ($150-$300 for after-hours), run through this checklist. Half of all AC service calls are solved by something on this list.
Check 1: Thermostat Settings (30 Seconds)
Sounds obvious, but check that the thermostat is set to COOL (not HEAT or OFF), the fan is set to AUTO, and the set temperature is at least 3-5 degrees below the room temperature. Dead batteries in a digital thermostat can kill the whole system — swap them and wait 5 minutes.
Check 2: Circuit Breakers (1 Minute)
Your AC has two breakers: one for the indoor air handler/furnace and one for the outdoor condenser. Check both at the electrical panel. A tripped breaker looks slightly "off center" — flip it fully OFF then back ON. Also check the outdoor disconnect box near the condenser — the pullout switch may have tripped or been left off after maintenance.
Check 3: Air Filter (2 Minutes)
A completely clogged filter can cause the evaporator coil to freeze, which shuts down cooling entirely. Pull the filter — if it's solid with dust, replace it or remove it temporarily (running without a filter for a day won't hurt the system, but a frozen coil will). Let the system thaw for 2-4 hours with the fan set to ON before restarting cooling.
Check 4: Outdoor Unit (2 Minutes)
Go outside and look at the condenser unit. Is it running? Is the fan spinning? If the fan isn't spinning but you hear a hum, the capacitor has likely failed — this is the #1 AC breakdown, and it's a $20 DIY fix. If nothing is running at all, check the disconnect box and breaker.
Check 5: Ice on the Lines (1 Minute)
Check the copper lines going into your outdoor unit. If the larger line (suction line) has ice on it, your system is freezing up. Turn the AC off, set the fan to ON, and let it thaw for 4 hours. Common causes: dirty filter (see Check 3), low refrigerant, or a failing blower motor.
Check 6: Drain Pan & Condensate (2 Minutes)
Many systems have a float switch in the drain pan that shuts down the AC when the drain is clogged. Find the drain pan under your air handler — if it's full of water, the drain line is clogged. Clear it by pouring a cup of vinegar into the drain access point, or use a wet/dry vac on the outdoor drain opening.
Check 7: The Reset Button (1 Minute)
Some outdoor units have a reset button on the high-pressure safety switch. If the system overheated and tripped the safety, pressing this button restarts it. Wait 30 minutes after shutdown before pressing reset to let pressures equalize.
Still Not Working?
If you've checked all seven and the system won't run, the most likely culprits are a failed capacitor, failed contactor, or failed condenser fan motor. All three are available with same-day shipping from National HVAC Parts and can be replaced in under an hour.
Use our free HVAC diagnostic tool for step-by-step troubleshooting, or chat with our tech Mike for part identification.