AC Unit Running But Not Cooling? 7 Things to Check Before Calling HVAC Service

It’s one of the most common summer complaints: the air conditioner is running, but the house isn’t getting any cooler.

Before assuming the compressor has failed, there are several things you can check that often solve the problem.

1. Check the Thermostat Settings

It sounds simple, but it happens all the time.

Verify:

• Thermostat is set to COOL
• Temperature is below room temperature
• Batteries are good (if applicable)

A thermostat issue can make it appear that the AC system has failed.

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1. Replace the Air Filter

A clogged filter restricts airflow and can cause poor cooling performance.

Signs include:

• Weak airflow from vents
• Longer run times
• Frozen indoor coil

Replace dirty filters every 1-3 months.

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1. Inspect the Outdoor Condenser

The outdoor unit must be able to release heat.

Check for:

• Grass clippings
• Leaves
• Dirt buildup
• Blocked airflow

Carefully clean the condenser fins if necessary.

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1. Look for a Frozen Evaporator Coil

A frozen coil prevents proper cooling.

Common causes:

• Dirty air filter
• Low refrigerant
• Blower motor problems

If ice is present, shut the system off and allow it to thaw completely before restarting.

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1. Check the Condensate Float Switch

Many HVAC systems have a float switch that shuts cooling off when the drain line becomes clogged.

Signs include:

• Indoor unit running
• No cooling
• Water in the drain pan

Clear the condensate drain and reset the switch.

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1. Test the Capacitor

A weak capacitor can prevent the compressor or fan from operating properly.

Symptoms:

• Outdoor unit humming
• Fan not spinning
• System starts intermittently

Capacitors are one of the most common HVAC repairs.

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1. Verify the Compressor Is Running

The compressor is the heart of the cooling system.

Warning signs:

• Outdoor fan runs but no cooling
• Loud buzzing
• Repeated clicking
• Warm air from vents

If the compressor isn’t operating, professional diagnosis is usually required.

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Most Common Causes Ranked

1. Dirty air filter
2. Clogged condensate drain
3. Frozen evaporator coil
4. Weak capacitor
5. Dirty condenser coil
6. Low refrigerant
7. Compressor failure

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Estimated Repair Costs

Repair Estimated Cost
Air Filter $10-$30
Drain Line Cleaning Free-$150
Capacitor $50-$250
Condenser Cleaning Free-$200
Refrigerant Repair $200-$1,000+
Compressor Replacement $1,000-$3,000+

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Final Thoughts

An AC that runs but doesn’t cool is often caused by airflow problems, clogged drains, frozen coils, or capacitor failures rather than a major system breakdown. Start with the simple checks before assuming the worst.

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