Why is my AC not cooling?

Q: How much does it cost to fix ac running but not cooling?

$150–$650. A diagnostic visit is typically $75–$200 and is often credited toward the repair. Capacitor replacement sits at the low end; refrigerant leak repair, coil work or compressor issues run considerably higher.

Q: Can I fix ac running but not cooling myself?

There are some safe steps to try first. Call a professional if the filter and outdoor unit are clean and it still won't cool, if you see ice, if the outdoor fan runs but the unit hums without cooling, or if it has been more than two years since a tune-up.

Short answer

An air conditioner that runs but doesn't cool is most often caused by a dirty air filter, a blocked outdoor unit, low refrigerant from a leak, or a frozen evaporator coil. Start by checking the filter and the outdoor unit — those two account for a large share of calls and cost nothing to rule out.

Urgency: Address soon
DIY: Some steps you can try
Typical cost: $150–$650
Time: 1–3 hours for most diagnostics and common repairs

Address soon

Not an emergency in mild weather. It becomes urgent during a heat wave, or if anyone in the home is elderly, very young, or has a health condition affected by heat.

What's happening

The system is powered and the blower is moving air, but heat isn't being carried out of the house. Either airflow is restricted, the refrigerant can't absorb heat properly, or the outdoor unit can't dump that heat.

Most likely causes

01
Dirty air filter
A clogged filter starves the system of airflow, which reduces cooling and can freeze the coil. Cheapest thing to check first.
02
Blocked or dirty outdoor unit
If the condenser can't release heat — because of leaves, grass clippings or a dirty coil — the system can't cool no matter how hard it runs.
03
Low refrigerant from a leak
Refrigerant isn't consumed. If it's low, there's a leak. Topping it up without finding the leak is a temporary fix.
04
Frozen evaporator coil
Ice on the indoor coil blocks airflow entirely. Usually a downstream symptom of poor airflow or low refrigerant.
05
Failing capacitor or compressor
The outdoor fan may spin while the compressor doesn't, so no heat is actually moved.
06
Thermostat set or wired wrong
Fan set to ON rather than AUTO circulates room-temperature air between cooling cycles and feels like a failure.

What you can try yourself

1Set the thermostat to COOL and the fan to AUTO, then set the temperature well below the room reading
2Replace the air filter if it's grey or you can't see light through it
3Clear at least two feet around the outdoor unit and gently rinse the fins with a hose
4Check whether the indoor coil or refrigerant line has visible ice — if so, turn the system off and let it thaw for a few hours
5Confirm the breaker for both the indoor and outdoor units hasn't tripped

When to call someone

Call a professional if the filter and outdoor unit are clean and it still won't cool, if you see ice, if the outdoor fan runs but the unit hums without cooling, or if it has been more than two years since a tune-up.

Who to call

HVAC technician

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What it should cost

$150–$650

A diagnostic visit is typically $75–$200 and is often credited toward the repair. Capacitor replacement sits at the low end; refrigerant leak repair, coil work or compressor issues run considerably higher.

Estimates are typical US ranges for orientation. Actual pricing varies by region, home and contractor — always get a written quote.

What happens if you wait

Running a system that can't cool wastes electricity and puts sustained strain on the compressor — the single most expensive part. A cheap capacitor or airflow problem left alone can turn into a compressor replacement or full system replacement.

Questions to ask the contractor

What specifically is causing the loss of cooling?
If refrigerant is low, where is the leak and are you repairing it or just recharging?
Is this repair worth it given the age of my system?
What's the warranty on the part and the labour?
Can you show me the readings you took?

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