AC Not Removing Humidity

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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 removing humidity, check the condensate drain line for clogs and ensure the evaporator coil is clean. Also, confirm the system is cooling properly and the fan speed is set correctly.

Confirm the symptom

High indoor humidity despite AC running
Visible condensation on walls or ceilings
Mold or mildew growth in the home
AC runs constantly but doesn't cool effectively
Musty or damp smell in the air

Tools and prep

Screwdriver set
Soft brush or vacuum with brush attachment
Flashlight
Plumber's snake or wire hanger
Gloves
Turn off power to the AC unit at the circuit breaker
Ensure the area around the unit is dry and well-lit

Step-by-step troubleshooting

Check Condensate Drain Line
Do: Locate the condensate drain line near the indoor unit and inspect for clogs.
Observe: Standing water or visible debris in the line.
Means: A clogged drain line prevents proper moisture removal.
Next: Clear the clog using a plumber's snake or wire hanger.
Clean Evaporator Coil
Do: Access the evaporator coil and gently clean it with a soft brush or vacuum.
Observe: Dust or dirt buildup on the coil.
Means: A dirty coil reduces humidity removal efficiency.
Next: Replace air filters if they are dirty.
Verify Fan Speed Settings
Do: Check the thermostat and AC settings for fan speed.
Observe: Fan is set to 'On' instead of 'Auto' or running at high speed.
Means: Incorrect fan speed can hinder humidity removal.
Next: Adjust the fan speed to a lower setting or set to 'Auto'.
Inspect for Refrigerant Leaks
Do: Look for signs of refrigerant leaks such as hissing sounds or ice buildup on the coil.
Observe: Hissing noises or frost on the coil.
Means: Low refrigerant levels affect cooling and humidity removal.
Next: Contact a professional HVAC technician for refrigerant recharge.
Check Air Filters
Do: Remove and inspect the air filters for dirt and debris.
Observe: Dirty or clogged air filters.
Means: Clogged filters restrict airflow, reducing humidity removal.
Next: Replace or clean the air filters as needed.
Ensure Proper Ventilation
Do: Check that all vents are open and unobstructed.
Observe: Closed or blocked vents.
Means: Poor ventilation affects airflow and humidity removal.
Next: Open and clear all vents to ensure proper airflow.

Common causes

Cause	Likelihood	Difficulty	Part often needed
Clogged Condensate Drain Line The drain line allows condensation to escape; a blockage prevents proper drainage.	Common	Easy	Plumber's snake or drain cleaner
Dirty Evaporator Coil Dust and debris on the coil reduce its ability to absorb moisture from the air.	Common	Easy–Medium	Soft brush or coil cleaner
Incorrect Fan Speed Settings A fan set to 'On' or high speed can blow air too quickly, reducing dehumidification.	Sometimes	Easy	None
Low Refrigerant Levels Low refrigerant reduces the system's ability to cool and remove humidity effectively.	Sometimes	Hard	Refrigerant recharge (professional service)
Clogged Air Filters Dirty filters restrict airflow, reducing the system's efficiency and humidity removal.	Common	Easy	Air filters
Poor Ventilation Blocked vents prevent proper airflow, affecting the system's ability to remove humidity.	Sometimes	Easy	None

Parts matching

Common parts needed to fix an AC not removing humidity include:

Plumber's snake or drain cleaner for clearing clogged condensate lines
Soft brush or coil cleaner for cleaning the evaporator coil
Air filters for replacing dirty or clogged filters
Refrigerant recharge kit (requires professional service)

Always turn off the power to the AC unit before performing any maintenance to ensure safety.

When to call a professional

If you find a refrigerant leak or suspect low refrigerant levels
If the evaporator coil is severely damaged or frozen
If the condensate drain line has recurring clogs despite cleaning
If the AC system is not cooling properly after checking all components
If you are unsure about any step or need specialized tools

FAQ

Why is my AC running but not removing humidity?

This can be due to a clogged condensate drain line, dirty evaporator coil, incorrect fan speed settings, or low refrigerant levels.

How often should I clean the evaporator coil?

It is recommended to clean the evaporator coil at least once a year to maintain optimal performance.

Can I use a store-bought drain cleaner for the condensate line?

Yes, but use it sparingly and follow the manufacturer's instructions to avoid damaging the system.

What should I do if my AC is making a hissing sound?

A hissing sound may indicate a refrigerant leak. Turn off the unit and contact a professional HVAC technician immediately.

How do I know if my air filters need replacement?

Check the filters monthly; if they are dirty or clogged, replace them with new ones.