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Cooling Coils in Your AC System: Keep Them Clean!

Air conditioners and heat pumps do their jobs by employing the phase-change properties of refrigerant gas in order to exchange indoor heat to the outdoors in the summer, creating cool air for your home – and in the case of heat pumps, also doing the reverse in the winter, delivering heated air. Crucial to the ability of your system to accomplish these jobs effectively, efficiently (lowest bills!), and reliably, are the two “coils” in the system known as the indoor evaporator coil and the outdoor condenser coil.

As refrigerant gas in your AC system circulates from the compressor that’s located in the outdoor unit to the outdoor coil, then to the indoor coil, and back around again, the “phase” of the refrigerant changes from a gaseous to a liquid state, and back again.

Simply put, this process works the magic that provides air conditioning. In the case of heat pumps when they’re in the heating mode, the direction is reversed but otherwise it’s nearly identical.

Locating Your Indoor & Outdoor Cooling Coils

Being able to locate and identify the cooling coils in your AC system can give you a better handle on how to help keep them clean and working properly. Both the indoor and outdoor coils are composed of many closely spaced aluminum fins bonded to small diameter copper piping — for optimal heat transfer. If you’ve seen a car radiator or looked closely at the sides of your outdoor AC unit, the aluminum fins are pretty easy to spot. The shape of the indoor and outdoor coils are different, but the finned tubing serves the same purpose in both components.

Where Is The Indoor Evaporator Coil Located?

In centrally ducted, forced air comfort systems, the indoor evaporator coil normally sits in a factory-built, insulated steel cabinet that connects inline to the ducting on the output side of the furnace or air handler. This configuration is called a “cased” coil, and in conventional upright installations the coil inside the case is often triangular in shape – hence the term “A-coil.” There are other coil configurations for horizontal and downflow furnaces.

In a finished installation, the evaporator coil is hidden from view inside the case and the ducting. At times, the coil may be located in a shop-fabricated sheet metal box, instead of a factory steel case.

For mini-split systems, the indoor coil is incorporated in each self-contained, independent indoor blower unit — installed as a major component inside the blower unit. Its shape is unique to the particular style of indoor blower unit, and in most cases can only be seen when the unit is opened for filter cleaning or servicing. Mini-split systems that employ an air handler are more similar to conventional central systems.

How to Identify Your Outdoor Coil

The outdoor condensing unit contains the heart of the AC system and its greatest electricity user, the compressor – along with an exhaust fan, related controls, and wiring. It also includes the system’s outdoor coil, known as the condenser coil.

The condenser coil is often easy to spot when performing a visual inspection of the outdoor unit. In the case of full-size, conventional central systems, this fin-tube coil can usually be seen wrapped vertically around three full sides of the outdoor condensing unit — located just behind the protective grille on the exterior of the unit.

Mini-split system outdoor units are very similar, although the outdoor unit is typically smaller and fairly compact, and you may need to look a bit closer to see the entire condenser coil.

What Happens If the Coils Get Blocked with Dust and Debris?

In order for your AC system to function properly, air must be able to flow freely through the spaces between the fin tubes in both coils. This allows for the efficient exchange of heat between the air and the refrigerant inside the copper tubing that the aluminum fins are attached to.

If airflow through either or both coils becomes restricted, usually as a result of dust, dirt, or other debris becoming lodged between the fins — this can significantly impact the refrigerant gas pressure in the sealed system and throw performance out of whack.

Clogged Coils: Higher Bills, Reduced Comfort – Or Worse!

When an indoor or outdoor coil gets heavily loaded or clogged, system efficiency (think utility bills!) and cooling effectiveness can be greatly diminished, and other undesirable consequences could result. This condition could even cause the system to stop operating. Have you ever heard the term “frozen coil?” That’s a perfect example of what could happen when coils get heavily loaded with all sorts of stuff. Unfortunately, getting a frozen system back online requires a little patience, but the results could be even worse – the repercussions could potentially come back to haunt you in the form of parts failures. The added stress simply isn’t good for your equipment, in the short and long term. Regular TLC can help you go a long way.

If it’s the indoor coil that gets loaded with dust, etc., this will also impact the actual airflow delivering cool air to the rooms in your home – in addition to impacting your cooling expenses. Rooms upstairs and those on the first floor located furthest from the furnace, will likely experience an even greater temperature difference than usual, compared to more central locations. The furnace blower may even be forced to run longer, almost constantly, in order to keep up with the thermostat temperature setting. Comfort levels drop. Not good!

Cleaning a Central System Evaporator Coil

In the case of a centrally ducted system, if your evaporator coil gets clogged with dust and requires cleaning, this initially involves removing the access door (cased coil) or accessing the coil by cutting a clean, appropriate size, resealable hole in the ducting. If you’re lucky, the coil may be able to be cleaned in place, or simply slid out a little, without having to remove it the system — but either way, it’s a time-consuming procedure. Cleaning is normally performed using a vacuum and a variety of specialty brushes.

If The A-Coil Needs To Be Removed

If it’s necessary to remove the coil from the system in order to properly clean it, an EPA certified technician must first recover the refrigerant gas from the system, and temporarily store it safely in an approved storage tank. Refrigerant recovery is done using a specialty recovery machine – which is required by law in order to prevent the refrigerant from leaking to the atmosphere.

In this near worst-case scenario, in addition to brushing and vacuuming, it may be necessary to also use an environmentally friendly cleaning solution in order to get the job done right. Regardless of the steps taken to get there, after the cleaning is complete, the evaporator coil is reinstalled in the ducting, and the refrigerant lines reconnected, the system is then recharged, leak-checked, and the gas pressures are checked during normal operation.

From beginning to end, this procedure is very labor intensive and can take up to an entire workday to complete.

Cleaning Mini-Split Evaporator Coils

When servicing a mini-split system, where the evaporator coil is incorporated in the indoor blower unit, the cleaning procedure can be equally involved as described above, albeit different in a number of ways because of the where coil is located. In a worst-case scenario, this could involve disconnecting the indoor unit from the system, as well as from where it’s currently installed, in order to properly access and clean its coil.

Cleaning Outdoor Cooling Coils

Outdoor condenser coils do not have an air filter protecting them like the ones protecting indoor evaporator coils — so the outdoor coil must be kept clean by regular attention from a qualified service technician. Properly and thoroughly cleaning the condenser coil primarily involves accessing the inside of the condensing unit and spraying with a garden hose through the aluminum fins and tubing, from the inside-out.

DIY homeowner types: Please keep in mind that while it’s better than doing nothing, hosing out your dirty condenser coil from the outside-in is not nearly as effective as the procedure described above. This is due to the direction the dirt or debris is coming from when it gets sucked between the fins. In addition, in some situations, an environmentally friendly cleaning solution may be needed to get the outdoor coil as clean as it should be.

How You Can Help Keep Your AC Coils Clean!

Protecting Your Indoor Evaporator Coil

The most common culprits for causing a clogged evaporator coil are furnace or air handler air filter issues, including the following:

• Forgetting to replace or clean the filter regularly. Once per season – much less once per year – is often not frequent enough! We continue to stress this important point
• The furnace filter was not setup and installed correctly when the system was originally installed. This could result in air bypassing the filter, defeating its purpose. The correct fix could potentially require corrective measures by an experienced service tech
• Poor quality air filter. You typically get what you pay for, and cheap replaceable filters may not do a good enough job; lots of them are rapidly going out of style. Even MERV8 rated, 1” disposable filters – while a step in the right direction – do not provide the level of filtration and protection currently recommended and used in many furnace replacements and new installations

• Replacement procedure in need of improvement. We occasionally find that a little better attention to detail by the homeowner, when replacing the filter, can help a lot. When you replace your air filter, make sure it’s snug in place and that the air returning to the furnace or air handler cannot go around and bypass the filter

Protecting Your Outdoor Condenser Coil: Routine Cleaning Is Key

Routine cleaning of the condenser coil is the answer to keeping your outdoor unit and its fin tube coil working up to speed. While there isn’t a standard schedule regarding how often the cleaning procedure should be done, annually is a good starting point. However, in some cases this may not be enough.

For example, if there are a lot of cottonwood trees nearby in your neighborhood — they are notorious condenser coil cloggers – it may be a good idea to have another outdoor coil cleaning visit after they’re done shedding their seeds, before the end of the cooling season. This would be a good thing to discuss with your technician when he or she comes out to perform maintenance. It’s not always necessary. In additon, if there are other trees, shrubbery, or flowers nearby that do the same, you should also keep a close eye on their potential impact on your outdoor unit.

Please contact me to schedule AC service, or to arrange for a free air cleaner install quote!