AC Is Cooling But Not Removing Humidity: 11 Possible Causes

Why is my house so humid with the AC on? If you are here right now to read this, you have a problem.

High humidity is something many people living in Florida have to contend with daily. When the relative humidity level rises above 55%, it can have many effects.

There are health effects of high humidity. Besides, too much moisture content in the indoor air can bring about a serious problem of mold colonies in the hidden spaces in your home.

As you can see, you have a reason to feel very worried when you have high humidity levels. However, even more worrying is having the AC running while still experiencing high humidity levels.

By design, the AC has an evaporator coil, which helps it draw moisture from the air. Temperature and humidity relationship is very close. Since warm air holds more moisture, when you turn the AC on to drop the room temperature, you expect the humidity to drop too. If this does not happen, there is a problem.


Why is my house so humid with the AC on?

Image of why is my house humid with the AC on

You could be asking: How does an air conditioner reduce humidity? There is a whole lot of science behind this.

However, it does this by passing the moist air over the evaporator coils. Since these coils have refrigerant, the moisture condenses and drips into a condensate pan. The now-dry air is released back into the house.

This goes on in air change cycles until the humidity level is lowered collectively in the whole room.

Here is a sneak peek at some reasons that can make your indoor humidity remain high even when the AC is running:

  1. Your AC unit is too big
  2. The evaporator coils are frozen
  3. There is debris on sensitive parts
  4. You have an old AC unit
  5. Air conditioning unit is due for repair and replacement of some parts
  6. You have been generating too much steam
  7. Your house is letting in humid air from outside
  8. When you do not set your AC unit correctly,
  9. AC runs on one speed only
  10. Your air ducts have leaks
  11. You have ignored the need for a dehumidifier

1. Your AC unit is too big

Image of ac running house still humid

Bigger is better when it comes to most home appliances and systems. However, in the case of air conditioning units, it appears bigger is not necessarily better.

When you have an air conditioning system that’s too big for your home, it cools the air pretty fast, maintaining the right room temperature.

To lower humidity, it needs to run long enough. If it can lower the temperature in short runs, it will not remove moisture from the air.

However, the evaporator coils inside the air conditioning unit need longer to pull the moisture from the air. Therefore, a large unit is most likely to switch off after amply lowering the temperature and allowing the humidity to build up.

So, how then will you know whether an air conditioner is too big for your home or room?

If it runs at short intervals of 10 to 20 minutes, well, it is too big. And that, dear home owner, is why the unit is doing a poor job of lowering humidity in your room.

When buying dehumidifiers and AC units, always get an appropriately-sized one. These systems have their own space rating. Do not go too small or too big. A slightly bigger unit can work okay.

You will need to find an HVAC company or technician to exchange the big AC system for a smaller one.

2. The evaporator coils are frozen

The evaporator coils of the air conditioner are usually more exposed than other parts of the unit. Therefore, they can develop frost easily.

Image of AC evaporator coils frozen

If this happens, the refrigerant that they carry is not going to condense the vapor so that the water can collect in the condensate pan while the dry air goes back into the house.

If this is the case, the AC will send back moist air into the room the same way it came in. Give the coils a check. Clean them if need be so that they can dehumidify your air.

3. There is debris on sensitive parts

The sensitive parts in this case are the coils, which are exposed. Even when there is no frost on the coils, with time, they are going to collect dust, dirt, and grime.

This is going to hinder them from working correctly, the same way that frost would make them unable to dehumidify the air.

The solution to this is to clean the coils, probably at regular intervals. In fact, it is best practice to clean the entire unit from time to time.

You can hire an AC technician to clean the entire unit professionally from time to time. They will also give it a run-over to see what needs replacing or fixing.

4. You have an old AC unit

ac running makes house humid

Age eventually catches up with everyone and everything, including your air conditioner. Now, the most usable, trouble-free years of an AC unit are between 10 and 15 years.

Therefore, if yours is older than 10 years and it can’t seem to do its work properly, think about replacing it.

Air conditioning units also come with warranties starting at 5 to 10 years. If the warranty has expired, your unit has probably run out of time.

Therefore, if you have been asking: How old should an AC unit be? If it is older than 10 years, well, it is gone.

Another thing that complicates older air conditioning units is a lack of spare parts. As these units are replaced with better and more modern units, it becomes harder to find replacement parts.

5. The air conditioning unit is due for repair and replacement of some parts

As a general rule, the HVAC system, including whole-house dehumidifiers, needs regular professional maintenance.

Hand-in-hand with the point we discussed on number 4 (unit age), if you are late with the regular maintenance of the unit, it could fail.

Sometimes, a lack of parts could cause delays. This could cause the unit to fail to dehumidify the air. If this happens sooner than later, the unit will also fail to control the temperature.

6. You have been generating too much steam

Image of AC unit not removing humidity

If you have been generating too much steam from cooking or taking hot showers, the humidity could spread all around the home.

In that case, the AC unit might not be able to work faster enough to lower the humidity level. If there is no humidity when you are not cooking or taking showers, the air conditioner is working okay.

When you do this consistently, your indoor space will always be humid, and this can cause mold.

If you dry your laundry indoors, the humidity can find its way out of the laundry area and into the rest of the house.

7.  Your house is letting in humid air from outside

Places such as Seattle have high humidity most of the time. Therefore, you may think the air conditioner is making the house humid, but the humid air could be coming in from outside.

During the summer, we want to keep the windows open to bring in more fresh air. However, if you live in a place that experiences high humidity, it will find its way into the house.

Rain increases the humidity. If there is rain outside and the AC is running indoors, you might think that it is not removing humidity. However, you should resume the right RH level when the rain stops and the moisture evaporates.

8. When you do not set your AC unit correctly

Image of air conditioning increasing humidity

You need to know whether you have set the fan to run and perhaps forgotten to get the AC to run. The fan will not be able to remove humidity.

You need to ensure that the settings you enter in the humidistat are right so that the AC runs.  When the fan runs alone, it might just whip humid air around, thus making no changes to humidity levels.

9. AC runs on one speed only

If you have an AC that runs on one speed setting only and just has the on and off function, it might be unable to remove humidity.

Cooling the air is faster, while removing humidity is harder. An air conditioner that just turns on when the temperature crosses the threshold and switches off when it lowers it to the set level might not have ample time to remove dampness from your air.

If it is the humidity season, you need to be able to keep your air conditioner running longer. This might hike the electricity bill but removing excess humidity has many benefits.

Lowering humidity will ensure there is no mold and will protect your clothes, electronics, walls, furniture, and other items from damage.

10. Your air duct have leaks

In number 7, we said that your home could be letting in humid air from outside. Another similar cause of air conditioners making houses humid is when there is a problem with the ductwork.

If there are leaks in the air ducts, the humidity level in your home will rise, and the air conditioning will not seem to be able to lower it.

Thus, if you have tried all of the things we have outlined here and they turned out fine, yet your house feels humid with the AC running, have a technician inspect your air ducts.

11. You have ignored the need for a dehumidifier

image of AC not working

Perhaps the reason why your house feels humid with ac running is that you lack a dehumidifier.

If your air conditioner only runs at one speed and just has on/off functions, it will never lower your indoor humidity very well. In that case, get a dehumidifier.

You can have an HVAC company install a whole house dehumidifier. However, these are costly to buy, install, and maintain.

There is an option, though, in the best portable dehumidifiers for the basement. These can remove a lot of moisture from the air. Besides, they come with a hose to drain water outside continuously.

If buying a large portable dehumidifier makes more sense to you, here are a few that you might want to try out:

Final Thoughts: Why Is My House So Humid with the AC On?

Is your house humid with the AC on? Well, you have seen 10 of the most possible causes for this.

This problem need not persist because, for each of the possible causes, we have given you a solution.

High humidity in your indoor space has many unpleasant effects on your health. It can trigger asthma, sinus problems and other respiratory illnesses.

If you live in a very humid place such as New Orleans, London, Kuala Lumpur, Jakarta, or any other, please invest in a high-capacity portable dehumidifier. It will help to control the humidity levels very well.