AC is Running but Not Cooling House (Troubleshooting Guide)

On this page

Quick answer
Confirm the symptom
Tools and prep
Step-by-step troubleshooting
Common causes table
Parts matching
When to call a pro
FAQ
Related guides

Quick answer

If your AC is running but not cooling, check the air filter, thermostat settings, and outdoor unit. A dirty filter or low refrigerant can cause this issue. Turn off the unit and call a professional if you can't identify the problem.

Confirm the symptom

AC fan is running
Indoor unit is blowing air
No cold air coming from vents
Outdoor unit is operating
Thermostat is set to cool

Tools and prep

Screwdriver set
Thermometer
Vacuum or brush
Gloves
Safety goggles
Thermal imaging camera (optional)

Step-by-step troubleshooting

Check Air Filter
Do: Turn off the AC and remove the air filter.
Observe: Is the filter dirty or clogged?
Means: A dirty filter restricts airflow and reduces cooling efficiency.
Next: Replace the filter if dirty.
Inspect Thermostat
Do: Verify the thermostat settings.
Observe: Is the thermostat set to 'Cool' and the temperature lower than room temperature?
Means: Incorrect settings can prevent the AC from cooling properly.
Next: Adjust settings if needed.
Clean Vents and Registers
Do: Use a vacuum or brush to clean dust from vents and registers.
Observe: Are vents and registers free of dust and debris?
Means: Blocked vents reduce airflow and cooling effectiveness.
Next: Ensure all vents are open and unobstructed.
Check Outdoor Unit
Do: Inspect the outdoor unit for debris and ensure it's running.
Observe: Is the outdoor unit clean and free of obstructions?
Means: Debris can block airflow and cause the unit to overheat.
Next: Clean the unit with a brush or hose.
Test Refrigerant Level
Do: Use a thermometer to check the temperature difference between the evaporator coil and return air.
Observe: Is the temperature difference within 15–20°F?
Means: Low refrigerant can prevent proper cooling.
Next: Contact a professional for refrigerant recharge.
Check for Frozen Evaporator Coil
Do: Turn off the AC and inspect the evaporator coil for ice buildup.
Observe: Is there ice or frost on the coil?
Means: A frozen coil indicates airflow issues or low refrigerant.
Next: Thaw the coil and address the underlying cause.

Common causes

Cause	Likelihood	Difficulty	Part often needed
Dirty Air Filter Restricts airflow, reducing cooling efficiency.	Common	Easy	Air filter
Incorrect Thermostat Settings Improper settings prevent the AC from cooling.	Common	Easy	None
Blocked Vents or Registers Reduced airflow leads to poor cooling performance.	Common	Easy	None
Low Refrigerant Insufficient refrigerant prevents proper heat absorption.	Sometimes	Hard	Refrigerant
Frozen Evaporator Coil Ice buildup restricts airflow and heat transfer.	Sometimes	Medium	None
Faulty Outdoor Fan Motor Improper outdoor airflow causes the system to overheat.	Rare	Hard	Outdoor fan motor
Worn Compressor A failing compressor cannot circulate refrigerant effectively.	Rare	Hard	Compressor

Parts matching

Common parts needed for this issue:

Air filter
Refrigerant (must be handled by professional)
Outdoor fan motor
Thermostat

Always replace air filters regularly to prevent future issues.

When to call a professional

If the refrigerant level is low
If the evaporator coil is frequently freezing
If the outdoor fan motor is not working
If the compressor is making unusual noises
If the issue persists after checking all basic components

FAQ

Why is my AC running but not cooling?

Common reasons include a dirty air filter, incorrect thermostat settings, low refrigerant, or a frozen evaporator coil.

How often should I replace my air filter?

Replace your air filter every 1–3 months, depending on usage and environment.

Can I recharge refrigerant myself?

No, refrigerant recharging requires specialized tools and must be done by a licensed professional.

What causes a frozen evaporator coil?

A frozen coil is usually caused by restricted airflow (dirty filter or blocked vents) or low refrigerant levels.

How do I know if my outdoor fan motor is faulty?

If the outdoor unit is running but not blowing air, or if you hear unusual noises, the fan motor may be faulty.