Your home's air conditioner generally needs to do three things to keep temperatures in your house relatively comfortable:

• Remove heat from the air
• Remote moisture from the air
• Distribute cooler and drier throughout your home

Dehumidifying your home will increase the apparent comfort level, but poor heat exchange at the evaporator or poor air distribution will cause the objective temperature to stay higher. When something restricts your system's airflow, your air conditioner will most likely struggle to reach or maintain your thermostat set point. Even worse, airflow restrictions can damage expensive AC components.

How Does AC Airflow Work?

Your home's HVAC system relies on a network of ducts to continually cycle air throughout the house. Every system will have at least one return vent and several supply vents. Your main house blower pulls air through the return vent or vents, moves that air across the filter and evaporator coils, and finally distributes the cooler, less moist air through the supply ductwork.

HVAC installers design home systems to meet specific airflow requirements. Any reduction in airflow can impact system efficiency, making it much harder for your air conditioner to keep your home comfortable. Additionally, the evaporator relies on adequate airflow for heat transfer. Restrictions can make the evaporator coils too cold, leading to icing.

What Causes Low Airflow?

The three primary causes of low airflow in any HVAC system are restrictions, fan issues, and leaks. Restrictions cause a pressure drop across the system, forcing the blower motor to work harder while pulling less air. On the other hand, the blower motor itself could be at fault due to mechanical problems or an incorrect setting. Finally, a leak in the system will reduce flow to the affected areas.

Restrictions are the most common problems and can result from simple issues, including a clogged filter or furniture placed on top of a vent. All vents should remain clear at all times, but it's especially crucial to keep return vents open. However, more severe restrictions can also exist. These problems include kinked flex ducts, collapsed ducts, or even poor ductwork installation.

While you can check for straightforward restrictions yourself, mechanical failures and leaks are trickier to diagnose. Leaks can be particularly problematic since they can exist almost anywhere in the system, including in ductwork behind walls or ceilings. A professional contractor will typically need to conduct an airflow test to determine if your system is leaking an unacceptable amount of air.

Although low airflow may seem like a relatively minor problem, it can cause big headaches. Allowing your system to run with reduced airflow for too long can stress expensive components in your system, reducing the life of your HVAC blower or even your AC compressor. If you notice your AC airflow dropping and can't find an obvious cause, it's time to call in a professional—such as Local Mechanical Heating & Air—for help.