Air Conditioning Work Safety Tip for Biofilm

Here are a few tips for staying safe while doing maintenance on Air Conditioners and Heat Pumps.

The Problem of Drain Clogging Slime


Biofilm is the slime that occurs in condensate drain pans, condensate pumps and drain lines which can lead to plugged drains, condensate back up and overflow. Biofilm can be clear, white, red, pink, or grey depending on its composition. Biofilms come mostly from airborne bacteria landing on surfaces where there is food, water, and shelter for them to live and reproduce. Bacteria eat organic material that get past the air filtration systems; they can hide in the shadows of UV lights and resist chemical attack. The bacteria excrete polysaccharides (long carbohydrate chains) or slime that envelopes the bacteria and protects it from being harmed. And if that weren’t bad enough, Biofilm slime has another defense mechanism that makes it a formidable opponent, contact with some Biofilms can make you very sick. Scientific testing has shown that biofilms are not easy to kill and will keep coming back as long as the bacteria have what they need to survive. Your job as an HVAC Professional doing maintenance, is to ensure that the system is clean and in good working order.  Here are some best practices for dealing with drain clogging biofilm.

Wet Vacuums:

A good portable wet vacuum with hose attachments is an important tool to have; they can be used to suck the slime out of drain pans, drain traps, drain lines and condensate pumps. Using a wet vacuum is a convenient way to quickly remove the slime from a drain system without cutting the pipes apart.

Wet Vacuums are the fastest and easiest way to remove biofilm, but they have the potential to cause harm to the technician and residents if used improperly.  Here are some ways to protect yourself and others.

  1. Never let your wet vacuum fill all the way up with dirty water because it could atomize the bacteria laden water and spread it into the air where it could be inhaled.  It is better to suck out the clogs and rinse the drains with lots of water.
  2. Never leave standing water in your wet vacuum where bacteria could multiply and always ask the homeowner where they would like you to dump the dirty water.
  3. Use clean water to flush out your wet vacuum and wet filter after every use.
  4. Use a disinfectant spray on your wet vacuum inside and out after every slime clean up.
  5. Open your wet vacuum and allow it to completely dry out once a week.

Proper Gear:

A mask and gloves are essential when dealing with biofilm since you don’t know what type of bacteria you are dealing with. Fortunately, this gear is abundant, inexpensive, and easy to get your hands on. Wearing an N-95 mask while working will prevent you from inhaling potentially dangerous bacteria.

Drain Lines:

Slime accumulation usually occurs where there is slow moving or stagnant water so getting your drains to completely empty is the best way to prevent the formation of biofilms. Drain lines should slope away from the furnace to the drain; a slope of ¼ inch per foot is recommended.

Drain Traps:

Evaporator drain traps are not needed on up flow furnaces and they create a perfect environment for biofilms to grow. Evaporator drain traps should only be used where the A/C drain pan is under negative pressure like they are in a rooftop unit or blower coil situation.

Condensate Pumps:

Condensate pumps are a great place for biofilms to grow so they should be taken apart and cleaned or sucked out and treated with chemicals every time you perform A/C maintenance. The reason that many pumps are not being cleaned on a regular basis is because they are hard to get apart. Many times, drain lines are inserted almost all the way to the bottom of the pumps; this should not be done. The drain lines should be inserted about ½ an inch into the pump which benefits you in two ways. First, the shorter pipes act as a sanitary air gap preventing any biofilm from climbing back up the drain lines and contaminating the system. Secondly, the shorter pipes let you disassemble the pump for easy cleaning without cracking pipes or joints.

If your pumps discharge line terminates at a standpipe it is a good idea to leave a sanitary air gap there as well. Many times, a discharge line will be pushed all the way down into a standpipe which will expose the discharge line to the dirty liquids in the soil pipe that can siphon back and contaminate the pump.

Chemical Treatments:

Biofilms are the body armor of bacteria and that makes them almost impossible to completely remove and if any bacteria remain, they will try to regrow. Chemical Treatments can slow down the progression of the biofilm, but it will not be a permanent solution. The best course of action is regular maintenance that includes removing as much of the biofilm as you can; then rinsing the area with plenty of water and finally treating the area with a chemical specifically designed for the job. Never spray a bleach solution on an A/C evaporator coil, bleach can damage the coil.

Nu-Calgon makes an EVAP Power-C product that has been designed for evaporator coil cleaning and they are recommended for all your biofilm clean up needs. See Fig. #1 

Nu-Calgon also makes Pan Treat tablets that can be installed in the drain pan that eliminate foul and musty odors. See Fig. #2.  They also make Gel Tab tablets that you place in the drain pan which will treat the water and help to prevent clogs that can cause overflow damage. See Fig. #3


                   Figure 1                                        Figure 2                                Figure 3


Contact the B-Y customer assurance team to learn more about work safety tips. 


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