Why Is My AC Running But Not Cooling? 8 Common Causes

Few things are more frustrating in an Oklahoma summer than hearing your air conditioner run all afternoon while the house keeps creeping warmer. The good news is that a handful of causes account for most of these calls, and a few of them you can check yourself in about ten minutes.

Start with these quick checks

1. Check the thermostat settings. Make sure it is set to COOL, not HEAT or FAN, and that the fan is on AUTO rather than ON. When the fan is set to ON, it keeps blowing even when the system is not actively cooling, which can push warm air through the vents. If your thermostat runs on batteries, swap them out. Weak batteries cause more strange behavior than most people expect.

2. Look at your air filter. A clogged filter is the number one cause of poor cooling we see. When air cannot move across the indoor coil, the system cannot remove heat from your home. If the filter is gray, dusty, or you cannot remember when you last changed it, replace it now.

3. Make sure the outdoor unit is running. Walk outside while the system is calling for cooling. You should hear the condenser running and feel warm air blowing out of the top. If the indoor fan is running but the outdoor unit is silent, see our post on outdoor units that will not run.

4. Check the outdoor coil. In Central Oklahoma, cottonwood fluff, grass clippings, dust, and red dirt can coat the outside coil and block airflow. If the fins look matted or dirty, turn the power off at the disconnect and gently rinse the coil with a garden hose from the inside out if you can, or from the outside with low pressure. Never use a pressure washer.

5. Make sure supply vents and returns are open. Closed vents and furniture blocking return grilles reduce airflow and can make the system struggle.

Problems that need a technician

6. Low refrigerant from a leak. Refrigerant does not get used up like gas in a car. If your system is low, there is a leak somewhere. Signs include ice on the copper lines, hissing sounds, and air that is cool but not cold. Topping it off without finding the leak only buys a little time.

7. A failing capacitor or contactor. These small electrical parts help the outdoor compressor and fan start. When they weaken, the outdoor unit may hum, struggle, or not start at all. They hold a dangerous electrical charge even with the power off, so please leave these to a licensed technician.

8. A dirty indoor coil or blower problem. Over time the indoor evaporator coil collects dust and the blower wheel can get caked with debris. Both reduce airflow and cooling.

How cold should the air coming out be?

A healthy system usually blows air about 15 to 20 degrees cooler than the air going into the return. On a 100 degree day, it is normal for a properly working system to struggle to keep a house below the mid 70s, especially in the late afternoon. If your house is 85 or warmer and climbing, something is wrong.

When to call Red Rock Mechanical

If you have changed the filter, checked the thermostat, and the system still is not cooling, turn it off to prevent further damage and give us a call. Running a struggling system for days can turn a small repair into a big one.

Red Rock Mechanical is a family owned HVAC and refrigeration company serving Oklahoma City, Shawnee, Bethel Acres, and the surrounding areas. Call us at (405) 305-3085 or book online. Your Comfort. Our Commitment.