When your AC stops cooling, it's natural to want to fix it yourself. Some problems really are simple — a thermostat setting, a clogged filter, a blocked vent. But opening the unit can turn a comfort problem into an electrical, mechanical or refrigerant hazard. Here are the four checks you can safely do, and how to know when it's time to call a pro.

First, check for danger

  • Smoke, flames, sparks or a burning smell: get everyone out and call 911. Don't open the unit.

  • Water near electrical equipment: stay away from the area and call for help.

  • Ice on the lines or unit: turn cooling off. Don't chip it or use heat on it.

  • A breaker that keeps tripping: stop resetting it — that's a sign of a fault.

  • Dangerous indoor heat: move elderly family members, infants and pets somewhere cool now.

The four safe checks

1. Thermostat

Make sure it's on, set to cool and set below the room temperature. Replace the batteries if the display says they're low, and write down any error code.

2. Filter

Check the filter you normally change. If it's clogged, replace it with the correct size and type. A badly clogged filter can choke airflow and even cause the coil to freeze.

3. Vents and returns

Make sure supply vents and return grilles are open and not blocked by furniture, rugs or curtains.

4. Outdoor unit

Clear leaves, debris and overgrown plants from around the outside of the condenser. Don't open it, reach through the grille, straighten fins or spray it with a pressure washer or chemicals.

If those four checks don't solve it, stop there and call a technician.

Why the rest is a job for a pro

Inside your AC are electrical parts that can shock you even when the system is off, fans that can start without warning and a pressurized refrigerant circuit. Please don't:

  • Remove panels or test electrical parts

  • Replace a capacitor, contactor, fuse or motor

  • Clean coils, straighten fins or oil motors

  • Pour chemicals down the drain line or bypass a float switch

  • Add refrigerant or hook up gauges — that requires EPA Section 608 certification

What to tell your technician

Good notes help, even though symptoms rarely point to one specific part:

  • Running but not cooling: the thermostat setting, indoor temperature, when it started and whether all rooms are affected.

  • Turning on and off a lot: roughly how long it runs and how long it's off.

  • Strange sounds or smells: what you hear or smell, and when.

  • Water or ice: where you see it.

For more on warning signs, read AC Not Cooling? Signs You Need an AC Repair.

What a good technician does

A qualified technician checks controls, airflow, temperatures, drainage, electrical parts, coils and refrigerant performance as needed, then explains what they found and why they're recommending a specific repair. If refrigerant is low, they should find out why — just adding more doesn't fix a leak.

About refrigerants

Older R-22 systems can still be serviced with reclaimed refrigerant, though it's costly. R-410A systems are still legal to run and repair. Newer refrigerants like R-454B and R-32 aren't drop-in replacements for either. See our R-410A guide for details.

Repair or replace?

A big repair or an older unit doesn't automatically mean replacement. Get the diagnosis and the repair price first; if replacement is worth considering, compare the two side by side. Our repair-vs-replacement guide walks through how to decide.

Checks didn't fix it? On Call's NATE-certified technicians have served Columbia and the Midlands since 2011. Our residential diagnostic fee is $89, waived when you go ahead with the repair, and you'll get a firm price before any work begins — plus in-person help with financing for bigger jobs. Learn more about AC repair, call (803) 781-4357 or request service online.