Air Conditioner Not Dehumidifying Well? A New Jersey Tech Explains Why | Air Experts

Have you cranked your thermostat way down but you still feel all sticky and sweaty? 

Wondering why your A/C isn’t dehumidifying your home?

To understand what’s going wrong, you need to know how your A/C normally dehumidifies your home. 

Normally your air conditioner lowers humidity by circulating your humid air over a cold evaporator coil (copper tubes).

These tubes condense the water vapor from the air and send it down a drain.

In other words, your air conditioner is a magnet for water vapor.  

But if your air conditioner isn’t dehumidifying the air properly, it’s probably because of one of these issues:

  • Thermostat is set to “ON” instead of “AUTO”
  • Dirty evaporator coil 
  • Leaky ductwork
  • Oversized air conditioning system

Issue #1: Thermostat is set to “ON” not  “AUTO”

Your home may be too humid because you’ve got your thermostat set on the wrong fan setting. 

Your thermostat’s fan setting controls the—wait for it— fan of your air conditioner’s blower. 

  • When set to “AUTO,” the fan only turns on when your home needs cooling.
  • When set to “ON,” the fan works 24/7—regardless of whether you need cooling or not.

The ON setting prevents your air conditioner from properly dehumidifying your home.


Well, remember when we said that your air conditioner is a magnet for water vapor? Normally the condensed water drops to a drain. However, when the fan constantly runs it circulates that water vapor back into your home.

Solution: Ensure your air conditioner’s fan setting is set to AUTO.

Issue #2: Dirty evaporator coil

The cold evaporator coil, which lives in your indoor A/C unit, is the part that cools/dehumidifies the air. It’s the “magnet” of water vapor.

However, if the coil is covered in dirt or dust, it becomes insulated from your air, meaning the coil can’t properly cool or dehumidify the air. 

Solution: Have a professional tech service your air conditioner once a year. The best time to get this done? Spring. You’re more likely to get service at a time that’s convenient for you since techs aren’t as busy during spring.

Also, it helps if you check the air filter once a month and change it as needed. The filter protects the indoor unit from dust. But once the filter gets all clogged up, your evaporator coil has no defense. It’s vulnerable to dirt all day long.

Issue #3: Leaky ductwork

Another cause of high humidity would be an abnormal source of humidity invading your home. One abnormal source would be through some leaky ductwork.

For example, if there’s a leak on the return side of your ductwork (the side sucking in air), that leak would cause your A/C to suck in the hot, humid air from your attic. 

Diagram of hot air getting into your ductwork via a leak.

Your A/C wouldn’t be able to condense all the extra water vapor. Meaning humidity levels stay high, making you feel sticky no matter how long the A/C runs. 

Solution: Have a technician investigate your home for air duct leaks and seal them as needed.

Issue #4: Oversized air conditioner

Finally, your A/C may not be dehumidifying properly because it’s oversized (too much cooling capacity).

An oversized unit cools your home too quickly. How can an A/C cool a home too quickly?  Isn’t it’s job to cool your home?

Yes, but it needs to do it at the right pace. You see, proper dehumidification takes time. To remove enough moisture for you to be comfortable, your A/C needs time to move enough volume of air over the cooling coil.  

Aside from high humidity issues, an oversized unit also:

  • Runs up your energy bills since it’s turning on and off more often (think of it like how you burn more gas to turn on your car)
  • Wears down the air conditioner more, reducing its life expectancy and increasing the chances of a repair

Solution: Contact a New Jersey air conditioner installer to see if your system is sized properly. They’ll have to do something called a Manual J heat load calculation.

If your system is oversized and about to kick the bucket, we suggest getting a new system that’s sized to meet your family’s needs. Check out our AC installation page for more details. 

Need Help from a New Jersey tech?

Contact us today and we’ll send over a cooling tech to help troubleshoot the issue!

Scroll to Top