What Are HVAC Evaporator Coils, Why Does Your AC Need Them, and What Malfunctions Can Thwart Your System?


Your home's central air conditioning unit runs on a fuel called refrigerant that needs to pass through a system of coils outside and inside your home to make your home a comfortable temperature. The evaporator coils are the interior set of coils that play a vital role in making sure the air coming out of your vents is cold.

What are the HVAC evaporator coils, why does your air conditioner need them, and what malfunctions involving the coils can thwart your system?

Evaporator Coil Function and Importance

The evaporator coils are located on a wall of the air handler portion of your air conditioner, which is usually housed inside the furnace to save space. The coils receive a liquid refrigerant delivered from the outdoor condenser coils through refrigerant lines and an inlet valve. The coils intake the liquid refrigerant and change it back into a gas, which causes the surface of the coils to become quite cold but not frozen.

A nearby blower fan passes ambient air across the coils then pushes that cooled air out your vents. Without the evaporator coils functioning, your air conditioner could still pump out air but that air would be warm instead of cooled.

Malfunction Threat: Inefficient Coil Phase Change

The evaporator coils receive the full supply of liquid refrigerant through the inlet valve, which ensures that not too much of the liquid enters the coils at one time. The careful allowance ensures that the coils can efficiently change the phase of all of the liquid to pass it back outside to restart the cooling cycle.

Evaporator coils can lose efficiency if the phase change is somehow disrupted. The efficiency loss will cause a gradual loss of cooling capability until your system is blowing out warm air.

A few different factors can cause efficiency loss: dirty or broken coils, the wrong type or amount of refrigerant, and a broken inlet valve that allows in too much refrigerant at once, or not enough refrigerant. If you're unsure of the cause, your best bet is to call in an HVAC sales and services technician for a service call.

Malfunction Threat: Freezing Coils

Evaporator coils can also become too effective, which causes the surface of the coils to freeze up. Subsequent passes of refrigerant won't undergo the proper phase change because the frozen surface throws off the calibration of the coils. Your unit might still put out cold air for a short time, but eventually the coils will thaw without any converted refrigerant to continue the process.

Frozen coils often happen due to dirt buildup on the coils or due to a refrigerant level or type issue. You can check the coils for dirt and use a no-rinse foaming coil cleanser, following the instructions closely, if you think dirt is the only problem. If you suspect a refrigerant issue, call in an HVAC tech like those at Triad Heating & Cooling Inc for assistance.

About Me

Learning To Program My Thermostat

Last summer, I realized that I didn't have the money anymore to keep paying steep power bills. My budget was stretched paper thin, and I was worried about how to make ends meet. One day, it occurred to me that the problem might stem from my air conditioning unit. I went outside and noticed that the sides were really clogged with dead leaves, dirt, and debris. I called my friend, who works as an HVAC contractor, to find out how to fix the problem. This blog is filled with articles about how to keep your HVAC system clean and perfect, so that you don't have to worry about a failing system.

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