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Why Is My Central Air Conditioner Not Blowing Hard?

June 21, 2017

Does the air coming out of your vent feel weak?

If so, check another vent to see if you still feel low airflow.

If you just feel low airflow in the 1 vent, you may have low airflow because of 1 or more of these 3 reasons:

  1. Crushed duct flex
  2. Disconnected or leaky air duct
  3. Closed damper

If 2 or more of your vents have low airflow, it’s likely caused by 1 of these 5 air conditioner problems:

  1. Dirty air filter
  2. Frozen evaporator coil
  3. Air duct problems
  4. Blower issues
  5. Blocked or undersized return vents

Let’s go into more detail about each of these issues and how to solve them.

3 issues that cause low airflow in one vent

#1: Crushed flex ducts

Many homes have flex ducts, which are very flexible wire tubes covered in plastic. However, because they’re so flexible, they can easily be crushed or smashed. A crushed flex duct will restrict airflow to a particular room or region of your home.

Solution: Go up in the attic to see if anything is pinching or crushing your flex duct. If you’re not sure what to look for, or just need an expert’s help, call an AC professional.

#2: Disconnected or leaky air duct

Over time, metal sheet ductwork and flex ducts can accidentally become disconnected or develop leaks. In fact, according to Energy Star, a typical house loses about 20–30% of the air that moves through the duct system due to leaks and poorly connected ducts.

Solution: Contact a professional to inspect your home’s ductwork for leaks and proper connection.

#3: Closed damper

Dampers are valves in your duct system that block or restrict airflow to a particular room. If they mistakenly get closed, they will restrict airflow to a room or particular vent.

Solution: If you have electronic dampers (you’ll see controls near your indoor unit), make sure they’re open and then see if that fixes the problem.

Still have weak airflow or can’t find your dampers? Contact an air conditioning expert to make sure your dampers are open.

5 AC problems that cause low airflow in multiple vents

#1: Dirty air filter

dirty vs. clean air filter photo

If your filter looks like the one on the right, it's dirty and you should change it

Believe it or not, something as simple as a dirty filter could be what’s causing your air conditioner not to blow hard. Without getting too detailed, a dirty air filter makes it hard for air to enter into your AC system, which means you’ll be feeling low airflow.

Solution: Check your air filter. If it’s dirty, replace it.

#2: Frozen evaporator coil

A frozen evaporator coil.

Your air conditioner has a component called an evaporator coil, which is the part that cools your air. If it gets too cold, moisture from your home’s air can freeze and form ice on the evaporator coil. This ice limits the flow of air into your home.

In addition to low airflow, you’ll know you have a frozen evaporator coil if you notice pools of water by your indoor unit.

Most of the time, a frozen evaporator is caused by 1 of these 2 issues:

  1. Low airflow issues (dirty air filter, blocked vents or malfunctioning blower)
  2. Low refrigerant levels, usually caused by a refrigerant leak

Read our article “Why Is Ice Building on My A/C Unit’s Pipes?” for more information.

Solution: First, turn off your AC so the ice can melt. Then, follow these steps:

  1. Change your air filter (if it’s dirty).
  2. Make sure all supply registers and return grates are open

If you do those 2 steps and your AC still freezes over, call a professional to check your refrigerant levels and take a look at your blower.

#3: Air duct problems

Your home’s air conditioning system depends on many interconnected ducts that look like a maze. If part of your ductwork is leaky, disconnected or bent, you could experience low airflow at multiple vents.

Solution: Contact an AC professional to inspect your home’s ductwork.

#4: Blower issues

A dirty blower, above, can decrease the amount of air that comes through your AC vents.

Your air conditioning system relies on a blower to pull in air from your home, run it over the evaporator coil, then push it back into your home as cold air.

If something’s not working right with your blower, you’ll feel low airflow. Some common blower issues that reduce airflow include:

  1. A dirty or clogged blower wheel
  2. A malfunction with the blower motor
  3. A problem with the blower motor capacitor
  4. A worn or loose fan belt (though this is very rare)

Solution: Contact and AC expert to inspect the blower and get it to run properly again.

#5: Blocked or undersized return vents

Your return vents should be unobstructed.

Take a look at your return vent (the big one that sucks in the air from your home). Is it closed, or is anything blocking it? If so, that could explain why your AC isn’t blowing hard.

Additionally, if your return vents were sized too small for your home’s air circulation needs, that would also create low airflow.

Solution: Make sure your return vents are open and clear of any obstructions. If the low airflow persists, contact a cooling/heating professional to take a look at your return vents to determine if they’re the right size.

Need a professional’s help in Denver?

Contact Plumbline to schedule an air conditioning repair. We’ll send one of our trusted experts to your home and get your AC working properly again.

We’ve been serving Colorado families since 1998.

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