An AC system that runs without cooling is one of the most frustrating calls we get in July. The equipment sounds fine. But the house will not drop below 80 degrees. Here are the five most common causes.
1. Dirty air filter
A clogged filter restricts airflow across the evaporator coil. The coil freezes, ice blocks airflow completely, and your system runs constantly without cooling. Check your filter first. If it is gray and matted, replace it, let the coil thaw for 2 hours with the fan running (not cooling), then restart.
2. Low refrigerant
Refrigerant does not get "used up" — low levels mean a leak. Signs: ice on the refrigerant line near the outdoor unit, reduced airflow, hissing or bubbling sounds. This requires a licensed technician to locate and repair the leak, then recharge the system.
3. Dirty condenser coils
The outdoor unit sheds heat through the condenser coils. A season of debris, cottonwood, and grime insulates the coils and prevents heat transfer. Annual cleaning resolves this. Do not spray a high-pressure hose directly into the coils — you will bend the fins.
4. Failing capacitor
Capacitors start and run the compressor and fan motors. A weak or failed capacitor is one of the most common summer repairs. The compressor may hum without starting, or the outdoor fan may spin slowly. A technician can test capacitors in minutes.
5. Oversized or undersized system
An undersized system runs constantly and cannot keep up on 95-degree days. An oversized system short-cycles — it cools fast, shuts off before dehumidifying the air, then restarts. Both feel like inadequate cooling. If your system was installed without a Manual J load calculation, sizing may be the root cause.
If none of these diagnose the problem, the refrigerant circuit, TXV, or compressor may need professional evaluation.