Why Is My AC Not Cooling?
An air conditioner that runs but fails to cool the house is one of the most common HVAC complaints. The good news: several causes are easy to identify before spending money on a service call. This guide walks through the most likely culprits from most to least common.
Check These Before Calling a Contractor
Many "not cooling" calls turn out to be simple fixes. Work through this list first:
- Thermostat settings: Confirm it is set to COOL, at least 5 degrees below current room temperature, and not stuck in a schedule mode. Replace batteries if it runs on them.
- Air filter: A clogged filter blocks airflow and can cause the evaporator coil to freeze, stopping cooling entirely. If it has not been changed in 90 days, replace it now.
- Circuit breaker: Find the AC breaker in your electrical panel. If it is tripped, flip it fully off then back on. Do not reset it more than once -- a breaker that keeps tripping signals an electrical fault.
- Outdoor unit: Go outside. Is the fan spinning? Is debris (leaves, shrubs, grass) blocking the unit? Clear any obstruction within 2 feet of the condenser.
- Ice on the lines: If the refrigerant lines or coil are iced over, turn the system off and set the fan to ON to defrost for 2-4 hours before restarting.
Most Common Causes
Low Refrigerant (Leak)
Refrigerant does not deplete on its own. If your system is low, there is a leak. Signs: air from vents is barely cool, ice on the lines or outdoor unit, hissing sounds. Fix: a technician finds and repairs the leak, then recharges the system. Cost: $200-$600.
Failed Capacitor
The capacitor helps start the compressor and fan. When it fails, the outdoor unit may hum but not actually compress refrigerant. Very common in summer heat. Replacement: $150-$350, usually same-day.
Dirty Condenser Coil
The outdoor coil expels heat. If it is clogged with dirt or cottonwood, it cannot release heat efficiently and the system runs constantly without cooling well. Annual cleaning prevents this.
Frozen Evaporator Coil
Usually caused by restricted airflow (dirty filter) or low refrigerant. Defrost by turning the system off, running the fan only for several hours. Address the root cause before restarting.
Failed Compressor
The compressor is the most expensive component. When it fails, there is zero cooling. On systems over 10 years old, replacement of the full unit often makes more sense than a compressor swap. See our repair vs. replace guide.
When It Is an Emergency
Call for same-day service when: outdoor temperatures are above 90 degrees F with elderly, infants, or medically vulnerable people in the home. A next-day appointment is fine when temperatures are moderate and alternative cooling is available.
Emergency service carries a $75-$150 premium. See the full AC repair cost guide.
Frequently Asked Questions
- Why is my AC running but not cooling?
- The most common causes are low refrigerant from a leak, a failed capacitor, a frozen evaporator coil from a dirty filter, a dirty condenser coil, or a faulty thermostat. Check the thermostat, filter, and circuit breaker before calling a technician.
- How do I know if my AC is low on refrigerant?
- Signs include: air from vents is barely cool or warm, ice forming on the refrigerant lines or outdoor unit, hissing or bubbling sounds, and higher electricity bills. Low refrigerant always means there is a leak -- it does not deplete on its own.
- What does it cost to fix an AC not cooling?
- Cost depends on the cause. A dirty filter is free. Refrigerant recharge: $200-$600. Capacitor replacement: $150-$350. Compressor: $800-$2,500. The diagnostic fee ($75-$150) identifies the actual cause.
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