One of the most common questions we get here at Carolina Cool is, “Why is my house humid when the AC is on?” There are a few potential reasons for this, which we’ll cover below. But first, let’s talk about why high indoor humidity is a problem. Too much indoor humidity can lead to health risks from mold and mildew, damage to the interior of your home, and damage to your HVAC system.

So, what causes high indoor humidity when the air conditioner is running? Here are a few possibilities:

• Frozen evaporator coils: If your evaporator coils are frozen, they can’t properly remove moisture from the air. This can lead to high indoor humidity, even when the air conditioner is running.
• Dirty unit or dirty air filter: A dirty air conditioner unit or filthy air filter can also restrict airflow and cause high indoor humidity. Dirt, dust and debris restricts air flow and makes your system work harder to try to remove moisture from the air before it is pumped out to the home.
• Wrong sized system: If your AC unit is too small for your home, it will run constantly and never reach the thermostat’s set point. This can cause the evaporator coils to freeze and lead to high indoor humidity. If your AC unit is too large for your home, it will cycle too quickly and not run properly, preventing it from removing moisture from the air as it is designed to do. Making sure you have the right size system for your home is key.
• High humidity outside: If the outdoor air is already humid, your AC unit will have a hard time removing all of the moisture from the air. Here in South Carolina, we experience very high humidity levels in the summer. If you have a problem with indoor humidity, you might need a dehumidifier unit added to your HVAC system to keep your moisture levels in check.
• Cooking inside without proper ventilation: Cooking indoors produces a lot of moisture. If you don’t have proper ventilation, this moisture can build up and cause high indoor humidity.

If you’re struggling with high indoor humidity, we recommend checking for these potential causes. Once you’ve identified the issue, you can take steps to fix it and improve your home’s comfort level. If you’ve worked to remedy these issues and still have issues with high humidity, you might want to consider a dehumidifier unit for your HVAC system to keep your indoor moisture levels under control.