Your AC is running but not cooling
Work through it in the order a technician would - cheapest and most likely first.
Is this an emergency?
Not an emergency, but don’t leave it a season.
You’re probably seeing
- The indoor fan is running, but the air from the vents is room temperature or barely cool
- The house is not reaching the thermostat setting, and the system never cycles off
- The outdoor unit is silent, or hums without the fan turning
- There is ice on the copper line or on the indoor coil
- Cooling has been getting slowly worse across the season rather than failing all at once
What it probably is
A clogged air filter
Most common, and the one fix that is genuinely yoursWeak airflow from every vent, and the filter is grey when you hold it to a light. On a badly blocked filter you may also find frost on the copper line at the indoor unit.
The outdoor unit has lost power
Common - and free if it is just a tripped breakerIndoor fan blows, but you hear and feel nothing outside. Check the breaker panel and the outdoor disconnect box on the wall by the condenser.
A failed run capacitor
Common - technician job, but a cheap partThe outdoor unit hums but the fan does not spin, or it starts and stops within seconds. This is the single most common failed part on a residential condenser.
Low refrigerant from a leak
Common - and always a leak, never normal consumptionIce on the copper suction line or the indoor coil, cooling that fades over weeks rather than failing suddenly, and a system that cooled worse each summer.
A frozen evaporator coil
Usually secondary - fix the cause, not the iceVisible ice on the indoor coil or the line, and little or no airflow. Usually a symptom of the filter or refrigerant problem above, not a fault in itself.
A failed compressor
Least common - but decides repair vs replaceOutdoor unit trips the breaker repeatedly, or runs with a loud mechanical knock and never cools. The expensive one, and the least likely.
What to do before anyone arrives
Set the thermostat to COOL and the fan to AUTO
Fan set to ON runs the blower continuously, which moves room-temperature air through the vents between cooling cycles. It feels exactly like "running but not cooling" and is not a fault.
Pull the air filter and look at it against a light
If you cannot see light through it, replace it. This is the most common cause on this list and costs a few dollars. Note the size printed on the cardboard edge before you go out.
Check the breaker for the outdoor unit, and the disconnect beside it
A central system is usually on two circuits - one for the indoor air handler, one for the outdoor condenser. Reset a tripped breaker once.
If the breaker trips again immediately, stop and call a technician. A breaker that will not hold is doing its job - it is reporting a fault in the circuit or the compressor, not misbehaving.
Look for ice on the copper lines or the indoor coil
If you find ice, turn the system OFF at the thermostat and leave the fan set to ON to thaw it. This can take several hours. Do not chip or melt the ice.
Running a system with a frozen coil can send liquid refrigerant back to the compressor. That converts a repair into a replacement.
Clear the area around the outdoor unit
Cut back growth to about two feet on all sides and rinse leaves and cottonwood off the fins with a garden hose from the outside in. A blocked condenser cannot reject heat.
Kill power at the disconnect first. Use a hose, never a pressure washer - the fins bend at surprisingly low pressure.
Stop here and book a technician
If the filter is clean, the breaker holds, and there is no ice, the remaining causes are the capacitor, the refrigerant circuit and the compressor. All three are behind a panel carrying line voltage and a capacitor that stores a dangerous charge even with the power off.
This is the end of the homeowner sequence. Everything past this point requires a meter, a certification, or both.
What it costs to fix
Ranges below are for the repair itself. For full replacement pricing see the hvac cost guides.
| What it is | What the part costs | What decides your bill |
|---|---|---|
| New air filter | A few dollars, any hardware store | Nothing - this one is yours, and no visit is needed |
| Tripped breaker reset | Free | Nothing, unless it trips again - then it is a diagnostic call |
| Dual run capacitor | About $10 retail for a common 45/5 MFD part | Almost entirely the visit and the labour, not the component |
| Refrigerant leak repair | Not a top-up - the leak is found and sealed first | Where the leak is. An accessible fitting is a different job from a buried coil |
| Compressor replacement | The major component in the system | Age and warranty status - this is the repair-or-replace decision point |
U.S. Bureau of Labor Statistics, Occupational Outlook Handbook (May 2025 wage data); retail part price from The Home Depot listing, retrieved 2026-09-14.
Read this table as the shape of the bill, not a quote. The reason we do not print a single installed price is that no primary source publishes one, and the aggregator figures that do are undated and unmethodical. What you can anchor on: the national median wage for HVAC mechanics and installers is $29.33 an hour (BLS, May 2025), and a diagnostic visit is billed on top. A capacitor quote is therefore mostly labour and truck time - which is legitimate, and also why a $10 part can appear on a several-hundred-dollar invoice. If a quote is far above that shape, ask what portion is diagnosis, what is labour, and what is parts.
Can I fix this myself?
The service panel on an outdoor condenser carries line voltage, and the run capacitor inside stores a dangerous charge for some time after the power is off. Do not open it. Separately: if you smell burning, see scorched wiring, or the breaker trips repeatedly, leave it off and call someone.
Reasonable to DIY
- Replacing the air filter
- Resetting a tripped breaker once
- Rinsing the outdoor coil and clearing growth around it
- Thawing a frozen coil by switching to fan only
- Checking that the thermostat is on COOL and the fan on AUTO
Call a pro
- Anything behind the condenser service panel, including the capacitor
- Any work involving refrigerant - by law, not by preference
- Finding and sealing a refrigerant leak
- Measuring superheat and subcooling to confirm the charge
- Compressor diagnosis, and the repair-or-replace call that follows
Two of the four common causes are genuinely yours to fix in ten minutes. The other two are not, and the refrigerant one is not a matter of skill or confidence: under the EPA Section 608 sales restriction, only a certified technician may buy R-410A. The small-can exemption people remember covers R-134a for car air conditioning and does not apply to a home system. If someone offers to "just top it off" without finding the leak, that is the wrong answer anyway - a sealed system does not consume refrigerant, so a low charge means it is escaping.
Is this covered by insurance?
Whether a claim is worth filing depends on the cause, your deductible and how the damage happened - not on the repair price alone.
Sources
Sources last checked
- Refrigerant Sales Restriction (40 CFR part 82, subpart F)U.S. Environmental Protection AgencyRetrieved 2026-09-14
- Section 608 Technician Certification RequirementsU.S. Environmental Protection AgencyRetrieved 2026-09-14
- Heating, Air Conditioning, and Refrigeration Mechanics and Installers - median pay, May 2025U.S. Bureau of Labor Statistics, Occupational Outlook HandbookRetrieved 2026-09-14
- Packard TITAN PRO 45+5 MFD 440/370V dual run capacitor - retail listingThe Home DepotRetrieved 2026-09-14
Sources for the figures and the legal requirements cited on this page.
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