Why Is My AC Not Cooling? 5 Causes and What Each Costs to Fix

Last updated: July 20, 2026 · Prices reviewed quarterly

An air conditioner that runs but will not cool almost always has one of a handful of causes — and the good news is that most AC-not-cooling repairs cost $150 to $600, with a national average near $350, per Angi and HomeGuide 2026 data. Only a failed compressor pushes you into four figures. Work the list in order — filter, power, thermostat, coils, refrigerant, compressor — because the cheap fixes are also the most common, and you do not want to authorize an $800 refrigerant job when a $20 filter was the problem.

AC Not Cooling: What It Costs to Fix, by Cause

Here is what each fix runs in 2026, cheapest first. A diagnostic service call is usually $75 to $150 and is often credited toward the repair if you hire the same company.

Likely cause	What goes wrong	Typical repair cost
Dirty air filter	Blocks airflow, can freeze the coil	$0 – $25 (DIY filter)
Thermostat fault	Miscommunicates with the system	$100 – $300
Dirty condenser coil	Cannot shed heat outside	$100 – $400
Failed run capacitor	Motor will not start	$120 – $400
Condenser fan motor	Outdoor unit cannot reject heat	$300 – $600
Low / leaking refrigerant	Not enough cooling capacity	$250 – $1,600
Failed compressor	The heart of the system dies	$1,800 – $2,800

Two things move these numbers. Parts are often the smaller half — a capacitor is a $15 to $40 component, so most of that $120 to $400 is labor and the trip charge. Warranty matters too: many compressors carry a 10-year parts warranty, so if yours is still covered you may pay only labor, which can cut a $2,500 job by a third or more. Ask the tech to check your model’s warranty status before you approve any big repair.

AC Not Cooling: The 5 Most Common Causes

1. A clogged air filter. This is the number-one cause and the cheapest to fix. A choked filter starves the system of airflow, which can freeze the evaporator coil into a block of ice that blows warm. Swap the filter, then give a frozen coil a few hours to thaw before restarting.

2. A power or capacitor problem. If the outdoor unit is silent or humming without spinning, suspect a tripped breaker or a failed run capacitor. A capacitor runs $120 to $400 installed, per This Old House — a same-day fix for a pro. Reset the breaker once; if it trips again, stop and call someone.

3. A thermostat fault. Dead batteries, a bad sensor, or wiring gremlins make the AC think the house is already cool. A thermostat repair or replacement is usually $100 to $300. Confirm it is set to “cool” and a few degrees below room temperature before assuming anything worse.

4. Dirty coils. The outdoor condenser coil dumps your home’s heat; caked in dirt and cottonwood, it cannot. A professional coil cleaning runs $100 to $400 and often restores cooling on its own. Rinse the outdoor unit gently with a hose (power off) as a first step.

5. Low or leaking refrigerant. A sealed system does not use up refrigerant — if it is low, it is leaking. That is why a simple “recharge” is a temporary fix; the leak has to be found and sealed. Freon leak repair runs $250 to $1,600, averaging around $800, per Angi. If your system still uses phased-out R-22, weigh replacement instead.

Check These Before Paying a Diagnostic Fee

Five minutes of checks can save you a service call. Confirm the thermostat setting and batteries, replace the air filter, make sure both the indoor and outdoor breakers are on, and clear leaves and debris from the outdoor unit. A clogged condensate drain can also trip a safety float switch and shut the system down, so check that the drain line is clear and the pan is not full. If the coil is iced over, shut the system off and let it thaw.

When to Call a Pro

Anything past the filter, thermostat, and breaker belongs to a licensed HVAC tech — and refrigerant work legally requires an EPA-certified one. Call a pro if the breaker keeps tripping, the unit hums but will not start, you hear grinding, or the air is still warm after your checks. Expect $75 to $150 an hour for labor, per HomeGuide.

The repair-or-replace line is age plus cost. If your unit is over 12 to 15 years old and the quote tops half the price of a new system — especially a compressor at $1,800 to $2,800 — replacing usually wins. See our AC unit replacement cost guide to run that math, or the whole-system picture in our HVAC replacement cost breakdown.

How to Prevent It Next Summer

Most no-cool calls trace back to skipped maintenance. Change the filter every 1 to 3 months, keep two feet of clearance around the outdoor unit, and rinse the coil each spring. A yearly HVAC tune-up catches a weak capacitor or low refrigerant before a July heat wave turns it into an emergency call at premium rates.

Frequently Asked Questions

Why is my AC running but not cooling?

The most common reasons are a clogged filter, a frozen coil, dirty condenser coils, a failed capacitor, or low refrigerant. Start with the filter and thermostat, then check the breakers. If the air is still warm, most repairs land between $150 and $600, per HomeGuide.

Why is my AC blowing warm air?

Warm air usually means the outdoor unit is not running (breaker or capacitor), the coil is frozen from poor airflow, or refrigerant is low. Confirm the thermostat is on “cool,” replace the filter, and let a frozen coil thaw before restarting.

How much does it cost to fix an AC that is not cooling?

Most repairs cost $150 to $600, averaging about $350, per Angi and HomeGuide. A capacitor is $120 to $400, refrigerant leak repair averages around $800, and a compressor runs $1,800 to $2,800. A diagnostic visit is typically $75 to $150.

Can low refrigerant stop my AC from cooling?

Yes. Low refrigerant means the system cannot absorb enough heat, so it blows warm and may freeze up. Because sealed systems only lose refrigerant by leaking, a lasting fix means finding and sealing the leak, not just topping it off — a $250 to $1,600 job, per Angi.

Why does my AC keep freezing up?

Ice on the coil comes from restricted airflow or low refrigerant. A dirty filter or blocked vents are the usual airflow culprits. Turn the system off to let it thaw, replace the filter, and if it re-freezes, have a tech check the refrigerant charge.

Should I repair or replace an AC that will not cool?

Repair a newer unit with a cheap fault. Lean toward replacement when the unit is over 12 to 15 years old or the repair — often a compressor at $1,800 to $2,800 — tops half the cost of a new system. Our AC and HVAC replacement guides help you compare.

Prices on this page are researched estimates compiled from the cited sources; your local costs will vary with market, access and scope. Always get multiple written quotes from licensed professionals before hiring.