AC Not Cooling
Why it happens and what to check first
When your AC is running but the air isn’t cool, a few common issues could be responsible. Learn what might be causing the problem — and the safe things you can check before calling a pro.
5 Common Causes of an AC That Isn’t Cooling
Open each section to see what may be happening inside your HVAC system and why it can affect cooling.
1 Dirty air filter Restricted airflow can reduce cooling performance and may contribute to a frozen evaporator coil.
What’s happening?
Your indoor blower needs to move a steady amount of air across the evaporator coil. When the air filter becomes heavily loaded with dust and debris, airflow can become restricted.
Why can this stop your AC from cooling?
With less warm indoor air passing across the coil, the system may remove heat less effectively. In more severe cases, the evaporator coil can become cold enough for moisture on the coil to freeze, which restricts airflow even further.
Inspect the filter and replace it if it is dirty. Make sure the replacement filter is the correct size and installed in the proper airflow direction.
2 Thermostat settings or thermostat issue An incorrect setting or thermostat problem can keep the system from cooling the home as expected.
What’s happening?
The thermostat tells your HVAC system when cooling is needed. If it is set to HEAT, OFF, or a temperature above the current room temperature, the cooling system may not receive a cooling call.
Why can this stop your AC from cooling?
The indoor fan can also run without active cooling in some thermostat settings. For example, FAN ON can keep air moving even when the outdoor cooling equipment is not operating, which may make the air coming from the vents feel warm or room temperature.
Make sure the thermostat is set to COOL and set several degrees below the current indoor temperature. FAN should normally be set to AUTO unless you intentionally want continuous air circulation.
3 Dirty condenser coil or blocked outdoor airflow Your outdoor unit must release heat. Dirt, vegetation, or blocked airflow can make that harder.
What’s happening?
After refrigerant absorbs heat from inside your home, that heat must be released outdoors through the condenser coil.
Why can this stop your AC from cooling?
If the outdoor coil is heavily covered with dirt or the unit is surrounded by leaves, weeds, grass, or other obstructions, it cannot reject heat as efficiently. Cooling capacity can drop and the system may operate longer and under greater stress.
Keep the area around the outdoor condenser clear. Do not open electrical panels or attempt internal repairs. Coil cleaning beyond light exterior debris removal is best handled during professional service.
4 Low refrigerant — usually caused by a leak Low refrigerant reduces the system’s ability to move heat and can contribute to evaporator-coil icing.
What’s happening?
Refrigerant circulates through a sealed system and transfers heat from inside your home to the outdoors. It is not something an air conditioner should normally “use up.”
Why can this stop your AC from cooling?
When refrigerant charge is too low, the system cannot absorb and move heat properly. The evaporator pressure and temperature may also fall enough for moisture on the indoor coil to freeze.
If you see ice on the refrigerant lines or indoor coil, turn the cooling system off and contact an HVAC professional. Finding and repairing the leak is important before properly recharging the system.
5 Electrical or control problem A failed electrical or control component can prevent one or more parts of the cooling system from operating.
What’s happening?
Your AC relies on several electrical components to start, stop, and control the indoor blower, outdoor fan, and compressor.
Why can this stop your AC from cooling?
Problems with components such as a capacitor, contactor, control board, wiring, blower motor, condenser fan motor, or compressor circuit can leave part of the system operating while another important component is not.
Do not open electrical compartments or touch capacitors, wiring, or control components. These areas can contain dangerous voltage and should be diagnosed by a qualified HVAC professional.
HVAC systems contain high-voltage components and refrigerant circuits that should not be opened or serviced by homeowners.