What is an Air Handler?

Your heating and cooling system is made up of many parts, all working together to keep you comfortable all year round. I’d like to talk about some of the components of your HVAC system—what they are and how they work. After all, the more you know about your system equipment, the better.


Let’s start with the air handler. An air handler is usually located in the garage, a closet, or in the attic (unless you have a package unit then the air handler is incorporated in the system). It is essential to any HVAC forced air system. All A/C units need a way to move the air, and the air handler serves this function. It houses the evaporator coils, the blower motor, and some HVAC controls. It can be an up flow, down flow, or horizontal flow AHU (air handling unit).

Knowing this information can help you find the filter if you have never changed the filter in this air handling unit. Some air handling units have the filter inside. If there is no filter in the return register or grill then the filter is either in the return duct or in the unit itself. Filtering the air is not only important for the indoor air quality in your home but it is essential for the proper operation of the air handling unit itself.

The evaporator coil carries refrigerant inside it. This coil and refrigerant, through the heat exchange process, absorbs heat from the air passing through the coils inside the air handler. The heat causes the refrigerant inside the evaporator coils to boil and change state. The refrigerant, where it enters the coil, is mostly a liquid. By the time it reaches the end of the coils it should have absorbed enough heat to change it from a liquid to a vapor. On the outside of the unit there are two copper lines. The large line is the suction line. This line carries the vapor (refrigerant) back to the compressor in the condensing unit. The small line is called a liquid line. This line carries liquid (refrigerant) from the condensing unit coils to the evaporator. When the unit is running the liquid line should be hot and suction line should be cold (unless it is a heat pump in the heating mode). The temperatures of these lines will vary depending on how hot the house is inside and the ambient temperature outside the home.

The blower is comprised of different components in most units. It has an electric motor, a blower wheel, and a cage typically referred to as a squirrel cage. Some air handling units have belt driven motors and most have capacitors for the air handler electric motor.

Your air handler is a vital piece of HVAC equipment. Next time, we’ll talk about how to maintain your air handler to keep it and your system operating efficiently.

Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems).For more information about Indoor Air Quality and other HVAC topics,click here to visit our website