AC Not Keeping House Cool: Fix It Yourself

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 isn't keeping your house cool, start by checking the air filter and thermostat settings. Clean or replace the filter if it's dirty, and ensure the thermostat is set to 'cool' and at a lower temperature than the room. If the issue persists, check for refrigerant leaks or a malfunctioning compressor.

Confirm the symptom

Thermostat is set to cool but house remains warm
AC runs continuously without cooling
Room temperature doesn't drop below 80°F
No cold air coming from vents
AC makes noise but doesn't blow cold air

Tools and prep

Screwdriver set
Thermometer
Vacuum cleaner with brush attachment
New air filter (if needed)
Safety gloves
Flashlight
Owner's manual for the AC unit

Step-by-step troubleshooting

Check Thermostat Settings
Do: Verify the thermostat is set to 'cool' and the desired temperature is lower than the current room temperature.
Observe: Thermostat displays correct settings and responds to changes.
Means: Thermostat is functioning correctly.
Next: Check Air Filter
Check Air Filter
Do: Locate and inspect the air filter for dirt or blockage.
Observe: Filter is clean or dirty.
Means: A dirty filter restricts airflow and reduces cooling efficiency.
Next: Clean or replace the filter if dirty.
Clean or Replace Filter
Do: Clean reusable filters with a vacuum or replace disposable filters with a new one.
Observe: Airflow improves after cleaning or replacing the filter.
Means: Clean filter improves airflow and cooling performance.
Next: Check Outdoor Unit
Check Outdoor Unit
Do: Inspect the outdoor unit for debris, leaves, or obstructions around the condenser coils.
Observe: Unit is clear of obstructions and coils are clean.
Means: Clear unit allows proper airflow and heat dissipation.
Next: Check Refrigerant Levels
Check Refrigerant Levels
Do: Listen for hissing sounds and inspect for oil stains around the unit, which may indicate a refrigerant leak.
Observe: No hissing sounds or oil stains are present.
Means: Refrigerant levels are adequate.
Next: Check Compressor
Check Compressor
Do: Listen for unusual noises from the compressor and ensure it's running when the AC is on.
Observe: Compressor runs smoothly without unusual noises.
Means: Compressor is functioning properly.
Next: Test System
Test System
Do: Turn on the AC and monitor the temperature drop over time.
Observe: Temperature gradually decreases to the desired level.
Means: AC is cooling effectively.
Next: Complete

Common causes

Cause	Likelihood	Difficulty	Part often needed
Dirty Air Filter A clogged filter restricts airflow, reducing cooling efficiency.	Common	Easy	Air filter
Thermostat Issues Incorrect settings or a faulty thermostat can prevent proper cooling.	Common	Easy	Thermostat
Refrigerant Leak Low refrigerant levels due to leaks prevent the AC from cooling properly.	Sometimes	Medium	Refrigerant
Malfunctioning Compressor A faulty compressor can't circulate refrigerant effectively.	Sometimes	Hard	Compressor
Dirty Condenser Coils Debris on condenser coils reduces heat dissipation, affecting cooling performance.	Common	Medium	None
Blocked Vents Closed or blocked vents restrict airflow and reduce cooling efficiency.	Sometimes	Easy	None
Overheated Outdoor Unit Excessive heat or lack of airflow around the unit can cause it to overheat and underperform.	Sometimes	Easy	None

Parts matching

Common parts needed for an AC not keeping house cool issue include:

Air filter
Thermostat
Refrigerant (must be handled by a professional)
Compressor
Condenser coils cleaning kit

Always refer to your AC unit's owner's manual for specific part requirements and installation instructions.

When to call a professional

AC still doesn't cool after checking all basic issues
You detect a refrigerant leak (hissing sound or oil stains)
Compressor is making loud or unusual noises
Thermostat is not responding to settings or changes
You suspect electrical issues or wiring problems
AC unit is over 10 years old and has frequent breakdowns

FAQ

How often should I replace my air filter?

Replace disposable air filters every 1–3 months, depending on usage and environment. Clean reusable filters monthly.

Can I recharge my AC's refrigerant myself?

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

Why is my AC running but not blowing cold air?

This could be due to a dirty filter, low refrigerant, a malfunctioning compressor, or a faulty thermostat.

How can I tell if my AC has a refrigerant leak?

Listen for hissing sounds and look for oil stains around the unit, which may indicate a refrigerant leak.

What should I do if my AC is making loud noises?

Turn off the unit and contact a professional, as loud noises may indicate a serious issue like a failing compressor or loose parts.