1. [Home](/) 2. [Guides](/guides/) 3. [Air conditioning through an Ohio summer](/guides/air-conditioning-guide/) 4. AC running but not cooling: common causes # AC running but not cooling: common causes When the air conditioner is running but the house will not cool, the cause is often simple. Some checks are safe for you to do, and some are not. ## Key takeaways - Start with the thermostat, the breaker and the air filter before anything else. - Ice on the indoor coil or copper line means you should turn the cooling off and let it thaw. - A dirty condenser can be rinsed gently with the power off, but a stopped fan is a job for a technician. - Low refrigerant means a leak, and it needs a certified technician to find and repair it. ## Start with the simple checks Before you assume something is broken, walk through the basics. They take a few minutes, and they solve more calls than you might expect. - Confirm the thermostat is set to Cool, with the temperature set below the current room temperature and the fan set to Auto. If the display is blank or dim, replace the batteries. - Check the breaker panel for a tripped breaker for both the indoor and outdoor units. Reset a tripped breaker once. If it trips again, leave it off and call a professional. - Look for a service switch on or near the indoor unit. It looks like a light switch and is sometimes knocked off by accident. - Make sure the supply vents and returns are open and not blocked by furniture, rugs or curtains. - Check whether the outdoor unit is running, and whether the fan on top is spinning. If all of that looks right and the air from the vents still feels warm or weak, continue through the causes below. ## A dirty filter and restricted airflow A clogged filter is the most common reason for a system that runs but does not cool well. The blower cannot pull enough air across the cold coil, so less air comes out of the vents, rooms heat up, and the system runs longer trying to catch up. Pull the filter out and hold it up to a light. If you cannot see light through it, replace it. Make sure the arrow on the frame points toward the blower. During cooling season, check it monthly, because summer dust, pollen and pet hair load a filter faster than you expect. A filter that is too restrictive for your system can cause the same problem, so if you have switched to a very dense filter and airflow dropped, ask an HVAC contractor whether your ducts and blower can handle it. Dirty blower wheels, closed dampers and crushed ducts also restrict airflow, and those need a professional. ## A frozen evaporator coil If the coil inside the indoor unit freezes, it can no longer absorb heat. You may see ice on the copper line that runs to the outdoor unit, water dripping near the indoor unit, or airflow that gets weaker over time. The most common causes are poor airflow from a dirty filter or blocked vents, and low refrigerant. In humid weather, ice can build faster because there is more moisture on the coil to freeze. If you see ice, switch the cooling off at the thermostat. Set the fan to On so air moves across the coil and melts it. Thawing can take several hours, and water may run down the drain line, so keep an eye on the area around the unit. Do not chip the ice off, because you can puncture the coil. Once thawed, replace the filter, open the vents and restart the system. If the coil freezes again, the cause is something other than a simple airflow problem, and it needs a technician. Running a frozen system can damage the compressor. ## A dirty or blocked condenser The outdoor unit has to release the heat the system picked up inside. If the coil is matted with cottonwood fluff, grass clippings or leaves, or crowded by shrubs, it cannot do that well. The system runs for long periods, the air from the vents is only slightly cool, and it may be worse on the hottest afternoons. Turn the power off at the disconnect next to the unit. Clear loose debris, then rinse the coil gently from the outside with a garden hose. Do not use a pressure washer, and do not stick anything into the fins. Keep a couple of feet of clearance around the unit. If the outdoor fan is not spinning, if the unit hums, or if the compressor is not starting, stop there. Those symptoms usually point to a failed capacitor, contactor or motor, and the electrical parts can hold a charge even with the power off. That is a repair for a technician, so schedule [AC repair](/services/ac-repair/). ## Refrigerant leaks and other jobs for a pro Refrigerant is sealed in a loop and does not get used up. If the charge is low, there is a leak, usually at a joint, a fitting or in the coil. Signs include ice on the lines, a hissing sound, oily spots at the connections, and cooling that has faded gradually. Handling refrigerant requires certification and the right equipment. A technician should find the leak, repair it and then recharge the system to the correct level. Adding refrigerant without fixing the leak is a short-term patch, and on older systems it may not be a sound investment. If your system is older, a good HVAC contractor will walk you through repair versus replacement options. Other causes that need a professional include a failed compressor, a bad capacitor, a stuck reversing valve on a heat pump, leaking or disconnected ducts, and a system that was sized too small for the house. If you have done the safe checks and the house still will not cool, [contact a contractor](/contact/) rather than letting the system run and strain. For the bigger picture of cooling season, see the [air conditioning guide](/guides/air-conditioning-guide/). ## Frequently asked questions Why is my AC blowing warm air? The most common reasons are a thermostat set to the wrong mode, a clogged filter, a frozen coil, a dirty condenser or a refrigerant leak. Check the thermostat and filter first. If the air is still warm, a technician should check the outdoor unit and refrigerant. Is it safe to keep running an AC with ice on the lines? No. Turn the cooling off and let the ice melt first. Running the compressor with a frozen coil can damage it, and the water from melting ice can overflow the drain pan. Can I add refrigerant myself? No. Handling refrigerant requires certification, and a low charge means there is a leak that needs repair. Adding refrigerant without fixing the leak does not solve the problem. 4 min read. ### Want us to handle it? R&W Heating & Cooling works in Lebanon, Mason, Springboro, Morrow, Waynesville, Mainville, Liberty Township, Centerville. [Get a quote](/contact/)[Call 513-932-6912](tel:+15139326912) ### More in this guide - [Air conditioning through an Ohio summer](/guides/air-conditioning-guide/) - [Why your upstairs is hotter than your downstairs](/guides/air-conditioning-guide/upstairs-too-hot/) - [SEER2 ratings explained simply](/guides/air-conditioning-guide/seer-ratings-explained/) ### Related services - [Air Conditioning Repair & Replacement](/services/ac-repair/) - [Ductless Mini-Splits](/services/ductless-mini-splits/) - [Tune-Ups & Maintenance Plans](/services/maintenance/) ### Service areas - [Lebanon](/areas/lebanon/) - [Mason](/areas/mason/) - [Springboro](/areas/springboro/) - [Morrow](/areas/morrow/) - [Waynesville](/areas/waynesville/) - [Mainville](/areas/mainville/) - [Liberty Township](/areas/liberty-township/) - [Centerville](/areas/centerville/) ### Other guides - [Furnaces and winter heating in Southwest Ohio](/guides/furnace-guide/) - [Heat pumps, humidity and indoor air quality](/guides/heat-pumps-and-air-quality-guide/) ## Call 513-932-6912 or send a quote request for repair, replacement or maintenance. [Get a quote](/contact/) [Call 513-932-6912](tel:+15139326912) --- **R&W Heating & Cooling** · 714 Columbus Ave, Lebanon, OH 45036 · 513-932-6912 [Get a quote](/contact/) · [Services](/services/) · [Guides](/guides/) · [FAQ](/faq/)