When your AC is not cooling, the most common causes are a wrong thermostat setting, a tripped breaker or a clogged air filter, according to Carrier, and you can check all three yourself. If those aren’t the problem, most repairs cost $150 to $650, while a new compressor can run $600 to $3,000 or more.
Prices checked on November 4, 2026. For safety, leave anything involving refrigerant or high-voltage parts to a licensed HVAC technician.
Quick checks when your AC is not cooling
- Thermostat: first of all, make sure it’s set to Cool, the fan is on Auto rather than On, and a schedule isn’t overriding your setting.
- Air filter: next, check the filter. The U.S. Department of Energy (DOE) recommends cleaning or replacing it every month or two during the cooling season.
- Breaker and disconnect: then look for a tripped breaker or blown fuse, and check the disconnect box near the outdoor unit. Carrier says to reset a breaker only if you’re comfortable doing so, and not to try again if it trips right away.
- Frozen coil: after that, look for ice on the copper lines or the outdoor unit, or extra water near the indoor unit. If you see ice, Carrier says to shut the system off immediately to prevent compressor damage.
- Outdoor unit: check that the fan is spinning and the unit isn’t clogged with dirt. In addition, DOE recommends trimming plants back at least 2 feet.
- Condensate drain: finally, a clogged drain can stop the unit from removing humidity and cause water damage, DOE warns.
If none of these fixes the problem, however, call a technician. Carrier’s FAQ also suggests waiting at least 30 minutes with the breaker off before you turn it back on.
Common causes of an AC not cooling and what repairs cost
| Repair | Typical cost |
|---|---|
| Service call or diagnostic fee | $75–$200 |
| Capacitor | $100–$400 |
| Contactor or relay | $100–$450 |
| Thermostat | $100–$500 |
| Drain line cleaning | $75–$250 |
| Outdoor fan motor | $200–$800 |
| Circuit board | $150–$800 |
| Refrigerant leak repair | $200–$1,500+ |
| Evaporator coil | $700–$4,500 |
| Compressor | $600–$3,000+ |
Low refrigerant or a leak
A low refrigerant charge always needs a technician. According to DOE, a technician should check the charge, test for leaks with a leak detector and recover any refrigerant instead of venting it. Meanwhile, HomeGuide puts leak repair at $200 to $1,500, plus $100 to $600 for a recharge.
Above all, don’t try this yourself, because Carrier warns against fixing refrigerant issues at home. Also, if your system still uses R-22, both HomeGuide and This Old House list that as a reason to consider replacing it. See our guide to AC refrigerant leak cost for details.
Frozen evaporator coil
If you find ice on the lines or the indoor coil, turn the system off right away, as Carrier advises, and let a technician find the cause. Meanwhile, DOE notes that technicians should measure airflow through the evaporator coil during service.
Electrical parts: capacitor, contactor and circuit board
These parts carry high voltage. As a result, Carrier says not to troubleshoot electrical issues yourself. Fortunately, they’re among the cheaper repairs, often $100 to $450. For more, read about AC capacitor replacement cost.
Dirty coils or a blocked outdoor unit
Coils also need regular checks. For this reason, DOE recommends checking the evaporator coil every year and keeping the outdoor unit clear. Moreover, HomeGuide lists coil cleaning at $100 to $400.
A failing compressor
Finally, the compressor is the most expensive part to replace, at $1,000 to $3,000 or more according to This Old House. Because of that cost, an older system may be better replaced. Our guide to AC compressor replacement cost compares both options.
Repair or replace an AC that’s not cooling?
To begin with, HomeGuide and This Old House use the same rule of thumb: multiply the repair cost by the system’s age in years. If the result is more than $5,000, replacing the AC usually makes more sense. They also suggest replacing it when it’s more than 10 to 12 years old, uses R-22, breaks down often or needs a repair worth half the price of a new unit.
For example, a $1,500 repair on a 12-year-old AC gives 18,000, well over $5,000. On the other hand, a $250 capacitor on a 6-year-old unit gives 1,500, so the repair is the better choice. For full replacement prices, see our AC replacement cost guide and our repair or replace guide.
How to avoid overpaying for an AC repair
- Ask about the diagnostic fee. Many companies apply it to the repair, according to HomeGuide.
- Book ahead when you can. HomeGuide lists emergency labor at $160 to $250 an hour, compared with $75 to $150 for standard hours.
- Check your warranty. Your manufacturer may cover the part, although usually not the labor. See our HVAC warranty comparison.
- Get it in writing. Also, ask for the part name, the price and the warranty on the repair before work starts.
Related guides: If the repair is expensive, run the numbers in our repair or replace calculator. If the unit also makes strange sounds, see our guide to HVAC noises.
AC not cooling: FAQ
Why is my AC running but not cooling?
The usual suspects are a dirty filter, a wrong thermostat setting, a frozen coil, a low refrigerant charge or an outdoor unit that isn’t running. So start with the quick checks above, and then call a technician.
Can I add refrigerant myself?
No. In fact, Carrier warns against fixing refrigerant issues yourself, and HomeGuide says refrigerant work should go to a licensed technician because refrigerant is toxic.
Should I turn off my AC if it’s not cooling?
Yes, if you see ice on the lines or coil. Carrier says to shut the system off immediately to avoid damaging the compressor.
How much does it cost to diagnose an AC that’s not cooling?
Generally, a service call costs $75 to $200, according to HomeGuide, and many companies credit it toward the repair.
Sources and review
Sources: Carrier, troubleshoot an AC not working (October 27, 2026); DOE Energy Saver, maintaining your air conditioner; HomeGuide, AC repair cost; This Old House, air conditioner repair cost (updated March 16, 2026). All checked on November 4, 2026.
Written by: HVAC Switch. Last updated: November 4, 2026. Read our editorial policy to learn how we research prices, or contact us if you spot an error.