AC Not Dehumidifying: How to Fix It

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 dehumidifying, check the condensate drain for clogs, ensure the evaporator coil is clean, and verify the thermostat settings. Regular maintenance can prevent this issue.

Confirm the symptom

High humidity inside despite AC running
Visible condensation on walls or ceilings
Mold or mildew smell in the home
AC runs continuously but doesn't cool effectively

Tools and prep

Screwdriver set
Vacuum with brush attachment
Flashlight
Thermometer/hygrometer
Safety gloves
Plastic scraper
Distilled white vinegar
Turn off power to the AC unit at the circuit breaker before starting

Step-by-step troubleshooting

Check Thermostat Settings
Do: Ensure the thermostat is set to 'Cool' and 'Auto' mode, not 'Fan Only'.
Observe: AC fan runs continuously if set to 'Fan Only'.
Means: Fan-only mode doesn't dehumidify; cooling mode does.
Next: If settings are correct, proceed to step 2.
Inspect Condensate Drain
Do: Locate the condensate drain line and check for clogs using a flashlight.
Observe: Standing water or algae in the drain line indicates a blockage.
Means: A clogged drain prevents proper moisture removal.
Next: Clean the drain with a wet/dry vacuum or vinegar solution if clogged.
Clean Evaporator Coil
Do: Remove the access panel and use a vacuum to clean dust and debris from the evaporator coil.
Observe: Dusty or dirty coils reduce dehumidification efficiency.
Means: Clean coils improve airflow and moisture removal.
Next: If coil is heavily soiled, use a coil cleaning solution.
Check Air Filter
Do: Inspect and replace the air filter if it's dirty or clogged.
Observe: A dirty filter restricts airflow, reducing dehumidification.
Means: Clean filters ensure proper airflow over the coils.
Next: Replace the filter and monitor humidity levels.
Verify Proper Airflow
Do: Ensure all vents are open and unobstructed, and check for duct leaks.
Observe: Restricted airflow or leaks can lower dehumidification efficiency.
Means: Unobstructed airflow is essential for proper dehumidification.
Next: Seal duct leaks and adjust vents as needed.
Test Humidity Levels
Do: Use a hygrometer to measure indoor humidity levels while the AC runs.
Observe: Humidity remains above 60% even after AC cycles.
Means: High humidity suggests a deeper issue with the system.
Next: If humidity doesn't drop, contact a professional technician.

Common causes

Cause	Likelihood	Difficulty	Part often needed
Clogged Condensate Drain Prevents proper drainage of moisture collected from the air.	Common	Easy	Condensate pump (if needed)
Dirty Evaporator Coil Reduces the coil's ability to absorb moisture from the air.	Common	Easy–Medium	Coil cleaning solution
Dirty Air Filter Restricts airflow, reducing dehumidification efficiency.	Common	Easy	Air filter
Improper Thermostat Settings Running in 'Fan Only' mode doesn't cool or dehumidify.	Sometimes	Easy	None
Low Refrigerant Levels Inadequate refrigerant reduces cooling and dehumidification capacity.	Sometimes	Hard	Refrigerant recharge (by professional)
Faulty Blower Fan Motor Inconsistent airflow affects dehumidification performance.	Rare	Hard	Blower fan motor
Malfunctioning Humidistat Incorrect humidity readings prevent proper dehumidification.	Rare	Medium	Humidistat replacement
Duct Leaks or Poor Insulation Leaks allow conditioned air to escape, reducing effectiveness.	Sometimes	Medium	Duct sealing materials

Parts matching

Common parts needed to fix an AC not dehumidifying include:

Air filter
Coil cleaning solution
Condensate pump (if needed)
Thermostat batteries
Duct sealing tape

Always purchase parts compatible with your AC model to ensure proper function and safety.

When to call a professional

Humidity remains high after cleaning coils and checking the drain
AC makes unusual noises or smells during operation
Refrigerant leaks are suspected (frost on the coil or hissing sounds)
Thermostat is old or unresponsive to adjustments
Blower fan motor is not functioning properly
Multiple components are failing simultaneously

FAQ

Can a dirty air filter cause my AC to not dehumidify?

Yes, a dirty air filter restricts airflow, which reduces the AC's ability to remove moisture from the air. Replace the filter regularly to maintain efficiency.

Why is my AC running but not reducing humidity?

This can be due to a clogged condensate drain, dirty coils, low refrigerant, or improper thermostat settings. Check these components first.

How often should I clean my evaporator coil?

Clean the evaporator coil at least once a year, or more frequently in dusty environments to maintain optimal performance.

Is it normal for my AC to not dehumidify in high humidity weather?

While ACs work harder in high humidity, they should still reduce indoor humidity. If they don't, there may be an underlying issue.

Can I use a dehumidifier with my AC to improve results?

Yes, using a dehumidifier alongside your AC can help maintain ideal humidity levels, especially in very humid climates.