AC not blowing cold air? What to check first and the likely causes

Air is moving, so the indoor blower works. The cooling half of the system is the part that has dropped out. Either the outdoor unit is not running, the refrigerant cannot move heat the way it should, or the thermostat is not asking for cooling at all.

The feel of the air tells you something. Room-temperature air usually means the compressor is not running. Slightly cool air that never gets cold points to airflow, a dirty outdoor coil or low refrigerant. Air that started cold and turned warm over a few hours often means the indoor coil has iced over.

1. Thermostat setting. Fan set to On blows air between cooling cycles, and that air feels warm. Heat mode, a schedule change or dead batteries cause the same complaint.
2. Clogged air filter. Restricted airflow cuts cooling and can freeze the coil.
3. Outdoor unit not running. A tripped breaker, a failed capacitor or a worn contactor leaves the indoor fan blowing uncooled air. A failed capacitor is one of the most common summer repairs; see what a capacitor replacement involves.
4. Dirty condenser coil. When the outdoor coil is matted with dirt or cottonwood, the system cannot reject heat and the supply air warms up, especially in the afternoon.
5. Frozen evaporator coil. Ice blocks the coil, so air passes without being cooled. The guide to a frozen AC coil covers thawing and causes.
6. Low refrigerant from a leak. Refrigerant is not used up like fuel. If the charge is low, it leaked out. Only a technician can confirm this with gauges and temperature readings.

Less often, the compressor itself has failed, or a duct has come apart in the attic and the cold air never reaches the rooms.

A technician starts with the same basics you did, then moves to measurements. Expect a check of the temperature drop across the indoor coil, the voltage and amp draw at the outdoor unit, a meter test of the capacitor and contactor, and refrigerant pressures and line temperatures.

If the charge is low, the right next step is to look for the leak. Adding refrigerant without finding the leak is a temporary fix that you pay for again. The refrigerant recharge cost guide explains what goes into that bill and why the refrigerant type matters.

Most causes on this list are ordinary repairs. Replacement enters the conversation when the fault is a failed compressor or a leaking coil on an older system, when the system uses R-22 refrigerant, or when this is one more large repair in a string of them. Ask for the diagnosis in writing, with the failed part named and the test readings noted, before you compare a repair against a new system.