Why Is My AC Not Cooling?
Start with the simple, safe checks: filter, thermostat, and airflow. If those are fine, the cause may need a technician.
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- Safe checks first
- Thermostat, filter, breaker
- Outdoor unit
- Clear and running
- Stop if
- Frozen coil or electrical smell
If your air conditioner runs but does not cool, start with the simple, safe checks: the thermostat setting, a clogged filter, blocked outdoor unit, tripped breaker, and closed vents. If those are fine, the cause may be refrigerant, the compressor, or electrical components that need a technician.
Safe things to check yourself
- Thermostat: confirm it is set to cool and below room temperature, and that the fan is on auto or on.
- Filter: a clogged filter restricts airflow. Replace it if it is dirty.
- Breaker: check whether the indoor or outdoor breaker has tripped.
- Outdoor unit: clear leaves and debris, and confirm it is running.
- Vents: make sure supply registers are open and not blocked by furniture.
- Frozen coil: if you see ice on the indoor unit or refrigerant line, turn the system off and let it thaw.
Do not open the equipment
Air conditioning equipment contains high-voltage components and capacitors that can hold a dangerous charge even when off. Do not remove panels or attempt electrical or refrigerant work.
When to call a professional
- The indoor coil is frozen repeatedly.
- The outdoor unit hums but does not start, or the breaker keeps tripping.
- You smell burning or see sparks.
- The system runs constantly but never reaches the set temperature.
If the equipment is old and repairs are adding up, see what size system you need before replacing it.
Sources and assumptions
This guide covers safe homeowner-level checks only. Refrigerant and electrical diagnosis require a licensed HVAC technician.
Frequently asked questions
- Why is my AC running but not cooling?
- Common causes include a clogged filter, a thermostat setting problem, a tripped breaker, a dirty outdoor unit, low refrigerant, or a failing compressor. Check the simple items first, then call a technician for the rest.
- Why does my AC freeze up?
- Frozen coils usually come from restricted airflow, such as a dirty filter or blocked vents, or from low refrigerant. Turn the system off to thaw, replace the filter, and call a technician if it happens again.
- Should I keep running my AC if it is not cooling?
- If it is not cooling and especially if the coil is frozen, turn it off. Running a system with a problem can cause more damage and raise energy costs.