Cleaning the coils on rooftop units may seem mundane, but it’s an important job that pays off for your customers in more efficient operation and longer living equipment. And, any job that’s worth doing is worth doing right.

The first step is to determine what type of condenser coil you’re working with. You may have a sectional coil, where two or three coils are attached at one end on a common tube sheet with the coils on the other end wire-tied together. The sections are typically one-pass thick. You’ll need to split these to clean them properly.

Or, you may be dealing with a standard coil, which can be a few inches thick, or possibly one of the newer microchannel-style coils, where using foaming cleaners is a no-no.


First, always be sure to lock out the power. Remove screws and panels as needed to allow access to the coil ends that are wire-tied together. Cut the wire ties carefully to separate the coils and support them as needed. Remove the blanket of cottonwood debris that builds up between coils by rinsing them with a hose or using a condenser brush. Soak the coils with water. Mix up a biodegradable foaming cleaner following the manufacturer’s mixing ratio.

Use a hand pump sprayer, or, preferably, a coil cleaner sprayer that sprays cleaner mixture and rinse water with one tool. Spray the cleaner from side to side and top to bottom, between each row from the exiting airside, if possible. Spray both sides of thicker coils. Let the cleaner foam out the dirt; this may take five or 10 minutes. Don’t let the cleaner dry. On larger coils, clean one section at a time. Rinse the coil and repeat, if needed.

When you’re done, always make sure to rinse off the customer’s roof. Restore the power to the unit and check its operation before moving on to the next one.


• Don’t Use Hot Water: Hot water could raise the refrigerant pressure and blow a relief valve. When you reassemble the rooftop unit, be careful not to accidentally screw through the cabinet into the condenser coil; and

• Don’t Use a High-pressure Washer: High-pressure washers may easily bend the fins. Typically, city water pressure is enough. Where city water pressure is low, we’ve used a small booster pump purchased from a local hardware store.


Always start by locking out power to the unit. Brush or rinse off cottonwood debris. Rinse the coil from both sides.

Apply cleaner to both sides, side to side, top to bottom, and in between each row. Let the cleaner foam out the dirt for five or 10 minutes. Don’t let the cleaner dry. Rinse the coil the same way you applied the cleaner, using a hose and low-pressure city water or a hand pump sprayer; be careful not to use a high-pressure stream that may bend the fins. Repeat if needed. Rinse off the customer’s roof. Restore power to the unit and check its operation.


Lock out the power to the unit. Rinse the coil from the exiting airside. Apply a mild biodegradable degreaser (not a cleaner; some cleaners are not recommended for use with microchannel coils) from side to side and top to bottom. Rinse and repeat, if needed. Be especially careful and gentle with these coils — no high-pressure water or scrubbing.

SIDEBAR: 13 Steps to a Clean Residential Evaporator Coil

Cleaning evaporator coils on your residential customers’ equipment is an essential task. We’re all well aware of the problems a dirty or clogged evaporator coil can cause. To ensure the job is done right, here are 13 essential steps to follow.

Step 1: Pump down the air conditioning condenser unit and/or evacuate the system.

Step 2: Remove the flare fitting, cut the line, and/or unsweat the connections from the indoor evaporator coil.

Step 3: Remove the plenum and carefully remove the coil.

Step 4: Remove the coil to the outdoor environment. Lightly remove large particulate off the inside and outside coil with a soft brush and vacuum. Be gentle. You don’t want to ruin the integrity of the fins on the coil, or damage the coil and cause a leak.

Step 5: Spray your preferred coil cleaning agent (there are several on the market) on the coil in a back-and-forth motion from left to right. Start from the top and move your way downward. Let it soak for about 15 minutes.

Step 6: Although most cleaning agents are self-rinsing, we recommend using a spray bottle full of water to rinse off any remaining particulate.

Step 7: Re-insert the coil into the plenum and reinstall the sheet metal.

Step 8: Ensure all connections are properly cleaned and de-burred. Reconnect the connections by either flare fitting and/or brazing. If brazing, we highly recommend purging the system with nitrogen to minimize oxidization from within the pipe.

Step 9: Pressure test the system using nitrogen and a soap test to ensure there are no leaks.

Step 10: Pull a vacuum to remove moisture and any contaminants from the system.

Step 11: You are now ready to refill the system. You can either release the refrigerant into the system that had been pumped down into the condenser, or fill the system with new refrigerant.

Step 12: Start the system and make sure the refrigerant level is properly balanced. (Properly balancing the system depends on a number of variables, including indoor wet bulb temperature, outdoor dry blub temperature, and if the system has a fixed orifice or thermal expansion valve.) After the refrigerant level is properly balanced, measure the external static pressure across the coil. This will ensure that none of the fins have been compromised and that all particulate has been removed.

Step 13: Check the ductwork for air leakage and seal up accordingly with silicone or putty.

Congratulations, you have now completed a thorough evaporator coil cleaning!

Sidebar information courtesy of Adam Tovey, service technician/home comfort advisor at Air Quality Dunrite, Toronto. The company was recognized in 2013 and 2015 by The NEWS as Canada’s “Best Contractor to Work For.” Contact him at For more information, visit

Publication date: 6/8/2015

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