AC Running but Not Cooling? 7 Things to Check

Work through this list in order before you call.

1. Check the thermostat settings

It sounds obvious, but it is one of the most common causes. Make sure the thermostat is set to Cool, the fan is set to Auto (not On), and the set temperature is actually below the room temperature. If the fan is set to “On,” it will blow air continuously, even when the cooling cycle is off, which can feel like warm air coming from the vents.

If the screen is blank or dim, replace the batteries.

2. Replace the air filter

A clogged filter chokes airflow. Less air moving across the coil means less cooling in your rooms, and in severe cases the coil can freeze. In Florida, check your filter monthly during summer. If you hold it up to a light and cannot see through it, change it.

3. Make sure vents and returns are open

Walk through the house. Supply vents should be open and unblocked by furniture or rugs. The return grille (the large vent that pulls air back into the system) should be clear. Closing vents in unused rooms does not save energy in most systems; it can actually reduce performance.

4. Look at the outdoor unit

Go outside while the AC is running. You should hear the compressor humming and see the fan on top spinning. Check for:

• Leaves, grass or debris packed against the sides
• A fan that is not spinning, or spins slowly
• A humming or buzzing sound with no fan movement

If the fan is not spinning but the unit is humming, turn the system off. A failed capacitor or fan motor can damage the compressor if the system keeps running. This is a job for a technician.

5. Check for ice on the coil or lines

Look at the copper refrigerant lines going into the outdoor unit, and if you can, at the indoor unit. Ice or frost means the evaporator coil is freezing. Common causes are a dirty filter, low airflow or low refrigerant.

If you see ice, turn the cooling off and set the fan to On for a few hours to thaw it. Do not chip at the ice. If it freezes again after thawing and changing the filter, call a technician.

6. Low refrigerant (a leak)

Your AC does not “use up” refrigerant. If it is low, there is a leak. Signs include warm air from vents, ice on the lines, a hissing or bubbling sound, and higher electric bills. Refrigerant work requires EPA certification, and simply adding refrigerant without fixing the leak only delays the problem. Our post on the AC refrigerant change explains what this means for older systems.

7. A failed part

Capacitors, contactors, fan motors and compressors all wear out, especially in Florida where systems run nearly year-round. A weak capacitor is one of the most common repairs we make: the system tries to run but cannot start the compressor or fan properly. Diagnosing failed parts takes professional testing tools.

Is it the heat, or is something wrong?

On extremely hot days, even a healthy system may struggle to keep up. A properly sized and working system should typically keep your home about 15 to 20 degrees cooler than outside. If it is 95 degrees out and your home is holding at 78, the system may be working as designed. If it is 85 out and your home is 82 and climbing, something is wrong.

When to call a professional

Call a licensed technician if:

• You see ice that comes back after thawing
• The outdoor fan is not spinning
• You hear buzzing, grinding or squealing
• The breaker trips when the AC starts
• You have checked the filter, thermostat and vents and it still is not cooling

Our AC repair service is available 24/7 across Broward County, including Sunrise, Plantation and Fort Lauderdale. The diagnostic is free when we do the repair.

If your system will not turn on at all, see our guide: AC stopped working at night? What to check first.