Why Is My Air Conditioner Not Dehumidifying? A Phoenix Tech Answers

2018 Sep 26
Posted in: Air Conditioning
why is my outside ac unit making a loud noise

The bottom line: Your AC has 2 jobs—to cool your home and dehumidify it.

So if you’ve noticed that your AC isn’t dehumidifying your home, you most likely have one of the following problems:

  1. Your thermostat fan is set to ON
  2. Your evaporator coils are dirty
  3. You have a refrigerant leak
  4. You have leaky ductwork
  5. Your system is oversized

We’ll explain each of these problems and how you solve them. First, though, let’s look at how your AC is supposed to dehumidify your home during normal operation.

Need a professional to inspect your AC and diagnose the issue?

Just contact us.

How your AC is supposed to dehumidify your home

During normal operation, your AC pulls in warm, humid air from inside your home. That warm air passes over very cold evaporator coils. Those coils are designed to pull both heat and moisture out of the air.

AC dehumidification process
 

An AC evaporator coil pulling heat out of the air.

After this process, all that’s left is cold, dehumidified air that gets pushed back into your home.

So what happens to all the moisture that’s absorbed from the air?

The moisture from the air slowly collects on the evaporator coils then drips down into a drain pan. As the water level in that drain pan rises, the moisture drains away outside via the condensate drain line (see below).

how ac removes moisture

The dehumidification process of an air conditioner.

So if your AC isn’t dehumidifying your home, there’s something wrong with this process.

Learn more about the AC process in our blog, “What Does an Air Conditioner Actually Do (And Why it Matters)”.

Let’s look at some of the reasons your AC might not be dehumidifying your home…

Possible reasons your air conditioner isn’t removing humidity

Your thermostat fan is set to ON

Before calling a pro, check your thermostat.

If you notice that the fan is set to ON, this is likely what’s preventing your AC from dehumidifying your home.

Why? Well, your AC fan is designed to run only during cooling cycles then shut off. When the fan shuts off, all the moisture absorbed by the cooling coils has time to collect and drain away outside (via the condensate drain line).

If the fan is blowing non stop, though, all that moisture sitting on the coils is blown right back into your home.

Related: ON vs AUTO: One of These Thermostat Settings Costs You Big Time

The solution: Make sure your thermostat fan is set to AUTO, never ON.

Your evaporator coils are dirty

Your evaporator coils are responsible for absorbing the heat and moisture from the air inside your home. But if they’re covered in a layer of dirt, they can’t do their job very well.

The result? Your AC will run longer and struggle to cool or dehumidify your home.

The solution: Have a professional inspect your evaporator coils and clean them if needed.

You have a refrigerant leak

Your air conditioner uses refrigerant to move heat and moisture out of your home and dump it into the outside air.

Over time, though, the lines that hold the refrigerant can develop leaks from normal wear and tear. If this happens, your AC has less cooling and dehumidification power.

Signs that your AC has a refrigerant leak include:

  • Higher levels of humidity
  • Your AC suddenly struggles to cool your home
  • You feel warm air coming from AC vents
  • You hear a hissing noise coming from AC lines
  • Your AC lines (or evaporator coil) is covered in ice

The solution: Have a professional inspect your AC lines for a leak, fix it and then recharge your system.

You have leaky ductwork

Almost all ductwork is leaky to some extent. In fact, Energy.gov estimates that the typical home loses upwards of 30% of conditioned air to leaks in ductwork.

The bad news is that if your ducts are located in the attic, basement or crawl spaces, these leaks could be pulling humid, dirty air into your home.

Signs you have leaky ductwork include:

  • Higher-than-normal monthly energy bills
  • Rooms that are tough to cool or heat
  • High indoor humidity levels
  • Excessive amounts of dust—even after you clean
  •  

Related: How Can I Tell if My Air Ducts are Leaking?

The solution: Have a professional inspect your ductwork to see if duct sealing would work for you.

Your AC system is oversized

If your air conditioner is too big for your home, you’ve likely always noticed high indoor humidity levels. You see, when an air conditioner is oversized for your home it cools your home quickly, shuts off then turns back on after a short period.

This “on-then-off-again” process is called short-cycling. Short-cycling prevents the AC from ever dehumidifying your home. That’s because the dehumidification process works best when the air conditioner has longer, steadier cooling cycles.

The solution: Have a professional inspect your home and AC system to determine if the unit is too big for your home. If it is, you may want to consider replacing it with a smaller unit.

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