10 May 2016
 Categories: , Articles

A frozen evaporator coil is one of the most common problems homeowners face when it comes to their A/C systems. A thick coating of frost can not only stop your A/C from cooling effectively, but it can also cause long-term damage to your system if the problem isn't fixed. The following explains the common causes of an A/C freeze-up, as well as tips you can use to fix the problem and prevent it from happening in the future.

How Ice Forms on the Evaporator Coil

While most people think air conditioners actively chill the air around them, the cooling process actually works by subtracting latent heat instead. The refrigerant inside of the evaporator coil pulls the latent heat inside and transports it to the condenser coil, where it's then released outdoors as exhaust heat.

As the air loses its latent heat, it also loses its ability to hold large amounts of water vapor. This dehumidifying effect condenses the water vapor into liquid drops that form on the evaporator coil and other surrounding surfaces. Many of these water droplets end up in the condensate drip pan, but only when the surface temperature of the coil is above the freezing point (32 degrees Fahrenheit).

If surface temperatures on the coil fall below freezing, the water droplets on the evaporator coil can freeze over and form a thin sheet of frost. Heavy amounts of frost can block air from flowing through the coil fins, preventing the coil from absorbing and transferring heat. This often leads to poor A/C performance and, if left to its own devices, eventual A/C failure.

What Causes Ice to Form

Poor air flow caused by a clogged air filter or a dirty evaporator coil can cause the evaporator coil to ice over. Without sufficient air flow, the evaporator coil can't grab as much latent heat as it needs to keep surface temperatures above freezing. A dirty evaporator coil actively blocks air flow by plugging up the aluminum fins on the coil.

A low refrigerant charge can also result in an iced-over coil. As refrigerant pressures drop, so does the temperature of the refrigerant itself. A good analogy to consider is what happens when a can of compressed air is steadily emptied. As more compressed air leaves the can, the can itself gets colder and eventually starts forming frost.

Breaking the Ice

The first step of dealing with an iced-over evaporator coil involves getting rid of the ice itself. First, check the air filter and change it if it's clogged or otherwise dirty. Next, turn off the A/C unit and set the HVAC system to run on fan mode. The air flow from the blower fan will gradually melt the ice.

You can speed up the process with a heat gun or hair dryer, but be careful not to concentrate too much heat on one area of the evaporator coil. Don't attempt to scrape, chisel or otherwise bash the ice off of the evaporator coil, as this could cause severe damage to the coil itself.

After melting the ice, take another look at the evaporator coil and make sure it's not caked with dust, debris or algae growth. In most cases, you can clean the coil on your own by sweeping it with a soft-bristle brush. To remove stubborn debris or algae growth, spray some foaming no-rinse cleaner on the coil. The foaming chemical action will dislodge the debris and the remnants of the spray will drip harmlessly into the drip pan.

If you're concerned about refrigerant leaks, you should have your HVAC technician take a closer look. Only your HVAC technician will have the tools and experience to properly check the refrigerant charge without releasing it into the air or causing significant injury. In many cases, your technician may use a UV dye to trace a potential leak back to its source.

Preventative Steps You Can Take

You can safeguard your A/C system against ice buildup by following the tips below:

• Change your HVAC air filter regularly - Changing the air filter at least every three months helps prevent clogs that can slow down and block air flow to the evaporator coil.
• Keep the evaporator coil clean - Regular evaporator coil cleanings can help prevent icing problems.
• Consider having your ducts cleaned - Your home's ducts can harbor a large amount of dust and debris. Consider having a professional clean your ducts on a regular basis.

These tips can help you save plenty of money on repairs and keep your A/C system ice-free. Talk to an HVAC contractor to get more advice on how to maintain your A/C unit.