Cleaning Your Air Conditioner's Evaporator Coil

Last week, I covered the basics of cleaning your air conditioner’s condenser unit and performing some basic maintenance. This week, I will cover the inside maintenance you’ll want to perform to clean your air conditioner’s condenser unit.

The inside maintenance on your air conditioner is just as important as the outside maintenance. Keeping your evaporator clean and free of corrosion will ensure that your unit operates efficiently year round. It will also allow you to spot potential problems before they lead to a major repair.

The inside unit is the evaporator, and it will be located near your furnace (if you have a furnace) or in your air handler if you have a heat pump. For this post, I’m going to assume that the evaporator sits on/near a furnace, but the steps for cleaning the evaporator are the same if you have an air handler instead.

Access your evaporator coil by opening the metal case that encloses it. The coil is often designed as an “A-frame” device, which means it has two panels that appear to lean toward each other (like the letter “A”). The evaporator panels will have thin metal fins on the outside and a series of copper tubes on the ends of the unit. The entire set-up will rest on a plastic (or metal) frame of channels that catch water and shunt it to the drain. The bottom of the evaporator is open to allow air to circulate from the blower motor of your furnace. Check the plastic frame for cracks, or if your unit has metal channels, check them for corrosion or rust. If a channel is cracked or rusted through, you’ll need to replace it to avoid damaging the rest of the furnace.

The evaporator’s job is to remove water from the air. On a very hot, humid day, your evaporator might eliminate several gallons of water from the air in your home, so it’s important to keep the condensate drain free-flowing at all times. Even though you’re condensing out “clean” water, biological matter can accumulate in the drain tube for your system and cause a backup. If your air conditioner is pulling gallons of water out of your home’s air and the tube that leads to your floor drain is clogged, you’ll find very quickly that you have drain problem AND a big mess to clean up!

Before you do anything on the evaporator, make sure the condensate drain is clear and free-flowing by running a little water in the catch basins at the bottom of your evaporator unit. If the water you add doesn’t flow freely to the drain, you can use a little Bio-Clean to clear out any accumulated biological debris in the drain. You can also use a solution of bleach and water to clear out any biologically active organisms in the drain.

Once you know the drain is fully open, examine the evaporator coils. If they’ve never been cleaned, or haven’t been cleaned recently, they’ll be coated with dust and other “inside” debris, like pet hair and cobwebs. You’ll need to make a decision about how well you can manually clean debris from the unit using the access you have. If you can’t get the fins clean without damaging them or the debris is crusted on, you may want to have a professional perform the inside maintenance. A badly clogged evaporator may need to be removed for cleaning, and that’s outside the realm of a do-it-yourself task.

You can find spray-on condenser coil cleaner at your hardware store or a home-improvement store. Usually, these cleaners are foaming and will break down debris and any greenish deposits that accumulate on the copper without needing a rinse. Spray the cleaner on the copper tubing and on the fins of the evaporator. The foaming cleaner will clean debris, return to a liquid state, and drain into the condenser pan on its own. You can use this when the air conditioner is running to get a little “rinse” from the water the evaporator is removing from the air. The cleaner takes just a few minutes to work, and you should be good to go, once you close the unit back up.

Change the air filter as long as you have the unit open. Just as in the heating season, you’ll want to change your furnace filter monthly to ensure that your system isn’t working harder than it has to. If you have questions about cleaning your evaporator unit, or you would like professional assistance, contact us at Boston Standard Plumbing & Heating at (617) 288-2911 to schedule an appointment. Also, you can “like” Boston Standard Plumbing on Facebook anytime!