--- title: "Why is my AC running but not cooling? | Root House Mechanicals" url: https://roothousemechanicals.com/resources/ac-running-not-cooling updated: 2026-10-05 business: "Root House Mechanicals" phone: "(615) 426-9344" text: "(615) 426-9344" email: info@roothousemechanicals.com hours: "Monday to Friday, 8 a.m. to 5 p.m." --- # Why is my AC running but not cooling? > The usual causes are a clogged air filter, a thermostat set wrong, an outdoor unit that has stopped, a frozen indoor coil or low refrigerant. Check the thermostat, the filter and whether the outdoor unit is running, including its breaker. If they all look right and the house still won't cool, call an HVAC technician. ## When to call a pro Call when the thermostat, filter and breaker all check out and the house still won't cool. Also call if: - the outdoor unit hums but its fan won't spin - a breaker for the system trips again after one reset - ice comes back after you've thawed the coil HVAC work is done by licensed and insured techs, and one call to us covers it. The visit to look is free, and you'll have a firm price before we start. Call or text (615) 426-9344, Monday to Friday, 8 a.m. to 5 p.m. - Call (615) 426-9344 (Monday to Friday, 8 a.m. to 5 p.m.) - Text (615) 426-9344 - Email: info@roothousemechanicals.com ## What should I check first? We'd start with the thermostat, then the air filter, then the outdoor unit. Make sure the thermostat is on cool and set below the room temperature. Set the fan to auto, not on. With the fan on, the blower runs between cooling cycles, pushing air nothing is cooling. That feels a lot like an AC that runs but won't cool. If the screen is blank or dim, swap the batteries. Then turn the system off and pull the filter. If it's up in the attic, go early in the morning and don't stay long. A filter caked with dust starves the system of air, and cooling drops off. If we had to bet on one cause, it's this one. ## How do I tell if the outdoor unit is running? Set the thermostat to cool, wait about 5 minutes, then go listen at the outdoor unit. You should hear a steady hum and see its fan spinning. Many systems pause a few minutes to protect the compressor, so give it time. If the fan inside blows but the unit outside stays quiet, you're moving air without taking any heat out of it. If nothing's running outside, check the panel for a tripped breaker labeled AC or condenser. If you smell burning, see scorch marks, or the panel is hot or wet, don't reset it. Call. Otherwise, turn the thermostat off, switch the breaker fully off and back on, and wait at least 5 minutes before going back to cool. One reset, no more. If it trips again, leave it off and call. A second trip means something on that circuit is drawing more than it should, and another reset won't change that. If the unit hums but its fan sits still, suspect a small part that helps the motors start and run (the capacitor). Sometimes it's the fan motor itself. Turn the system off at the thermostat, since the compressor needs that fan to shed heat. If it keeps humming anyway, switch off its breaker, leave it off and call. ## Why is there ice on my AC lines or coil? Ice usually means the indoor coil isn't getting enough air across it, or the system is low on refrigerant. Ice on an air conditioner in July looks backwards, but it's a useful clue. The indoor coil runs cold on purpose, and warm air moving across it keeps it above freezing. Cut that airflow with a dirty filter, closed or blocked vents or a weak blower, and it ices over. Low refrigerant does it too. Less refrigerant means lower pressure in the coil, and lower pressure means a colder coil. To thaw it, switch the thermostat off and put in a clean filter. Then set the fan to on, with cooling still off, and lay towels down for the meltwater. The moving air melts the ice, which can take a few hours. If the fan won't run, leave everything off and call us. Once it's fully thawed, try cooling again. If the ice comes back, it's likely a refrigerant leak, a dirty indoor coil or a blower problem. Turn cooling off and call us. ## Does my AC need more refrigerant? Only if it's low, and low usually means a leak. An air conditioner doesn't burn through refrigerant the way a car burns gas. It's a sealed system, so if yours cooled fine for years and is low now, it's escaping, often at a coil or a joint. Less often, a system was undercharged when it was installed. Adding refrigerant without fixing the leak means paying for it again later. If an AC needs a top-off every summer, that refrigerant is going somewhere. The real fix is finding and repairing the leak, then charging to the manufacturer's numbers. That's [AC repair](https://roothousemechanicals.com/hvac/ac-repair) work. This one isn't DIY. Anyone who works on the refrigerant side of an AC, or buys refrigerant for one, needs EPA Section 608 certification. ## Can a dirty outdoor unit keep the AC from cooling? It can cut cooling a lot. The outdoor unit dumps the heat your AC pulls out of the house, and it needs open air to do it. Grass clippings, leaves, cottonwood fluff and dirt pack into its thin metal fins (the coil) and hold that heat in. Keep plants, fences and anything you store outside about 2 feet back, and keep the space above the unit open. The unit's installation manual lists the exact clearances. With the breaker off, you can pull leaves and clippings off the outside by hand. Leave the coil itself to a spring [HVAC tune-up](https://roothousemechanicals.com/hvac/hvac-maintenance). The fins bend easily, and a bent fin blocks air just like dirt does. ## Why does my AC struggle on the hottest days? Because a properly sized system is designed around a typical hot summer day, not the hottest few afternoons of the year. On the worst July afternoons in Middle Tennessee, a healthy system can run nonstop and still fall a little behind. If the house catches up by evening, that's usually normal. Warm air from the vents isn't. Neither is a system that never catches up overnight, or a house that feels clammy. Those can trace back to leaky ducts in the attic or crawl space, low refrigerant or a system sized wrong for the house. If it happens on ordinary summer days too, or you're not sure, call us. ## Safety first Turn the system off at the thermostat before you change a filter. Before you reach in around the outdoor unit, switch off its breaker too. The thermostat doesn't cut its power. Don't open the outdoor unit's panels or the electrical box beside it. They hold high voltage, and one part inside (the capacitor) can shock you even with the power off. Don't chip or scrape ice off a frozen coil. One slip can puncture it, and then you have a refrigerant leak. Let it thaw. ## Common questions ### How often should I change my air filter? Check it monthly in summer and change it when it looks gray. Most 1-inch filters last 1 to 3 months, less with pets or a system that runs all day. A thicker 4-inch media filter can go 6 to 12 months. ### Why is there water around my indoor unit? Usually a clogged drain line or a coil that's thawing. Your AC pulls water from the air and drains it away. If that line clogs, water backs up, and many systems have a switch that shuts cooling off. That can look like the AC just quit. Thaw water stops once the ice is gone. If there was no ice, or it keeps coming, turn cooling off so no more collects, wipe up and call us. ## Related services - [AC Repair in Middle Tennessee](https://roothousemechanicals.com/hvac/ac-repair) - [HVAC Tune-Ups and Maintenance in Middle Tennessee](https://roothousemechanicals.com/hvac/hvac-maintenance) Written by Root House Mechanicals. Last updated 2026-10-05.