AC Running But Not Cooling

When your AC runs constantly but the indoor temperature never reaches the setpoint, the system is producing some cooling — just not enough. The cause is almost always one of: undersized system, dirty/restricted airflow, leaking refrigerant, leaking ductwork, or failing components reducing capacity. Here's how to figure out which.

Most Likely Causes

1. Refrigerant low (slow leak)

A system that's down 15–20% on refrigerant will still cool — just weakly. Run times grow, the temp split between supply and return shrinks, and the house never reaches setpoint on hot days.

2. Major duct leak in attic

If your ductwork has come loose or developed seam leaks in the attic, you might be cooling 130° attic air instead of return air from the house. We've seen homes lose 30% of their cooling capacity to a single disconnected duct.

3. Outdoor coil completely fouled

A condenser coil that hasn't been cleaned in years can drop heat-rejection capacity by 25–40%. The compressor runs hot, the system can't dump heat, and you get warm-ish air inside.

4. Compressor wearing out

Old compressors lose efficiency. They'll keep running for years past their prime — just with less and less cooling output. If your system is over 12 years old and gradually losing performance, this is likely it.

5. Undersized system (or new load)

A 2.5-ton system can't cool a 2,400 sq ft house in Texas no matter how new it is. If you've added a sunroom, blown out an attic, or had three new occupants move in, the existing system may simply be too small for the new load.

6. Thermostat in a bad location

A thermostat mounted in the coolest hallway of the house will satisfy quickly while the bedrooms stay 80°. Common in spec homes.

Try These Steps Before You Call

• Replace the air filter.
• Walk every room and check that supply registers are open and not blocked by furniture.
• Look at the outdoor unit — clean coil with garden hose if visibly dirty.
• Listen for the compressor (the deep hum) — it should run continuously when calling for cool.
• Check the temperature differential: stick a thermometer in a supply vent vs return grille. A healthy system shows a 16–22°F difference. If yours shows less than 14°F, something is reducing capacity.

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