AC running but not cooling the house

Both halves of the system are running, so this is a capacity problem. The AC is removing some heat, just less than the house needs. That separates it from an AC that is blowing warm air, where the cooling side has stopped working entirely.

Weather matters here. An air conditioner is sized for a typical hot day in your area. During an unusual heat wave, a healthy system may run nonstop and let the indoor temperature drift up in the late afternoon, then recover in the evening. If the house falls behind on ordinary summer days, or it kept up last year and does not now, something has changed.

1. Restricted airflow. A dirty filter, closed registers, a dirty evaporator coil or a weak blower. The air at the vent feels cold but there is little of it.
2. Dirty condenser coil. The outdoor coil cannot shed heat, so the system loses capacity exactly when it is hottest outside.
3. Low refrigerant. A slow leak reduces capacity gradually. You notice longer run times first, then ice on the line.
4. Duct leaks. A disconnected or leaky duct in an attic or crawl space dumps cooled air outside the living space and pulls hot air in.
5. Undersized or aging system. An addition, new windows facing west, or lost attic insulation can push the load past what the AC was sized for.
6. Worn compressor. A compressor that runs but no longer pumps efficiently cools weakly even with a full charge.

Expect measurements, because this symptom cannot be diagnosed by eye. A technician compares the return and supply air temperatures, checks static pressure or airflow, and reads refrigerant pressures and line temperatures to see whether the charge is correct. They will inspect both coils and look over accessible ducts.

If the evaporator coil is impacted with dirt or leaking, cleaning or replacing it is a larger job because of where it sits. The evaporator coil replacement cost guide explains what drives that price.

You cannot verify refrigerant charge, coil condition or duct leakage yourself. Gauges, airflow tools and access to the coil are required, and connecting gauges to the system is restricted to certified technicians. Say so on the phone and describe the pattern: when it falls behind, how long that has been happening, and what you already checked.

Dirty coils, filters and duct repairs are maintenance-level fixes, and they often restore the cooling you remember. Replacement becomes a fair question when the compressor is worn, when the coil is leaking on an older system, or when the system was too small for the house from the start. In that last case no repair will help, and a proper load calculation should come before any new equipment is quoted. The AC repair overview covers how to weigh a large repair against a new system.