Source: https://oncallsc.com/articles/how-to-repair-an-ac-unit-a-comprehensive-guide # AC Troubleshooting: 4 Safe Checks Before You Call a Pro Four safe checks you can make when your AC stops cooling, the warning signs that need immediate action, and what to leave to a professional. Fact checked September 26, 2026July 6, 2026 ![Technician kneeling outdoors using a multimeter to test the electrical wiring of an open air conditioning condenser unit.](/img/asset/YXNzZXRzL2xlZ2FjeS1ibG9nL2ViODllMzFkYzA0OS1hcnRpY2xlXy00MjY1NzA5MzQwMzE1NjA0NjM2XzBfOTQwOTE0NTI0NzEyMDAuanBn/eb89e31dc049-article_-4265709340315604636_0_94091452471200.jpg?w=960&fm=webp&s=c21186a942acdbdaefc70247754c205a) 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](https://oncallsc.com/articles/ac-not-cooling-signs-you-need-an-ac-repair.md). ## 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](https://oncallsc.com/articles/r410a-refrigerant-phase-out.md) 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](https://oncallsc.com/articles/ac-repair-vs-replacement-columbia-sc.md) 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](https://oncallsc.com/hvac-services/air-conditioning-repair.md), call (803) 781-4357 or [request service online](https://oncallsc.com/contact-us.md). ## Sources & updates - [U.S. Department of Energy — Air Conditioner Maintenance ](https://www.energy.gov/energysaver/air-conditioner-maintenance) - [ENERGY STAR — HVAC Maintenance Checklist ](https://www.energystar.gov/saveathome/heating-cooling/maintenance-checklist) - [EPA — Section 608 Technician Certification ](https://www.epa.gov/section608/section-608-technician-certification) - [EPA — Homeowners and Consumers: Refrigerant FAQs ](https://www.epa.gov/ods-phaseout/homeowners-and-consumers-frequently-asked-questions) - [EPA — Frequently Asked Questions on the HFC Phasedown ](https://www.epa.gov/hfcs/frequent-questions-phasedown-hydrofluorocarbons)