Monday, May 18, 2015

Cleaning Condensate Lines

In the southeast, it is a given that the evaporator condensate line will get clogged with slime. The only questions are how long will it take and how messy will it be to clean up? What we often did in the past was to cut out the section of drain near the coil, blow out the drain line, and rebuild the drain with new PVC ells and pipe. However, that means the owner is constantly paying for you to rebuild something that should be cleanable. That is why every evaporator condensate line should have a way to open the drain to facilitate cleaning. In fact, this is now required in the most mechanical codes. You can add cleanout spots by replacing ells with tees, or by using a manufactured product made just for that purpose. Rectorseal and MSD Research both market drain cleanout devices which make complying with the mechanical code and cleaning the drain easier. Ideally, you should be able to clean out the line in both directions – from your cleanout to the evaporator and from your cleanout to the outside.

A Gallo gun using CO2 charges works well for blowing out the drain line. Nitrogen does a good job too, but getting a nitrogen cylinder to the cleanout spot can be difficult. Another option is a sludge sucker. It uses nitrogen to create a vortex, which sucks the condensate and goo out of the drain line. The sludge sucker typically connects to the drain outlet. Some techs use wet vacs and connect to the drain outlet, or to points on the condensate cleanout. Even if the drain is not stopped up, clearing the evaporator condensate line should be part of normal service. Don’t make the customer call you back later because the condensate line plugged up.


  1. Carter, Great article. The ALL-ACCESS device Model AA1 can also be used as a vent so you can do away with the pvc vent after the trap. By removing the schrader cap and valve core the AA1 is a cleanout and air vent. It can be installed after the trap and you have both the vent and cleanout in one device.

    Please take a look at the ALL-ACCESS A/C Condensate Cleanout Device Model AA1.
    The website is at
    It shows how it saves Service Technicians time clearing drains and also allow access to add drain line cleaners or tablets.
    It meets the New ICC IMC 307.2.5 & IRC M1411.3.3 “Drain Line Maintenance Code” for 2015.
    This Short Video explains how it works:
    They are Available at Most HVAC Distributors.
    Thank you!

  3. Trent Technologies just donated two of their CostGard drain system which we'll be installing during the summer session. It is a dry drain system that has three connections. One to the drain, one to the return section and the third to the blower compartment. They have one video where they put a wet oatmeal concoction in the drain pan to simulate slime and you can see in the video that slime does not flow out but is ejected. It costs more than field fabricated traps but considering the damage cost to ceiling sheet rock or drop ceiling should be worth consideration.

  4. I think the gallo gun is a really good tool for cleaning. I would love to get my hands on one. This summer I am going to clean my HVAC unit and I am sure it would help.

  5. Sometimes people forget about cleaning the evaporator condensate line or don't realize the lines dirty faster in certain parts of the country. Float switches turn off A/C units with clogged lines to avoid leaks and water damage; anyone who has an A/C unit that does not automatically shut off when the line clogs should get a HVAC professional to install a float switch.

    Lane Pemberton @ Metcalfe Heating & Air Conditioning

  6. Great DIY blog! We recently had our AC unit refurbished after several years of no issues. Now, however, we have had some trouble with the fan bearings making a bit of noise. So we will need to look into that in the future. We'd definitely keep in mind all your re-gassing tips and tricks!

    Ambrose @ Brown & Reaves Services, Inc.