Friday, 15 June 2018
Clean Condensate Lines to Prevent Mold

Foul odors coming from your cooling system are more than an unwelcome inconvenience – they can be downright dangerous.  Air conditioner smells are most often caused by mold and mildew growing somewhere within the system.  In this post, we’ll look at how your HVAC system can harbor mold and be responsible for circulating musty odors.




Air conditioners work primarily by dehumidifying the air.  The water drawn out of the air drips from the evaporator coils into a condensation pan (or drip pan) under the HVAC air handling unit. Drip pans are the perfect environments for mold and algae growth, which then can clog the drain lines.  If the moisture is unable to flow out of the system, the water backs up and can overflow the drip pan, causing water damage in your home as well as causing your air conditioner to shut off.  In fact, a clogged condensate drain line is the second leading cause of AC failures. 

Regular Maintenance is Essential

As part of regular spring/summer HVAC maintenance, the evaporator coil and condensation lines are cleaned.  Having your system’s evaporator coil cleaned not only works to reduce smell, but the procedure will also improve the efficiency of your air conditioner. The mold, mildew, and dirt deposited on your coil will reduce airflow through the system, lowering its efficiency, and causing your HVAC to fail sooner.

Clean Condensate Pan & Drain Lines

But even if you’ve had your system cleaned at the beginning of the season, the condensate drain line could still become clogged during the course of use.  So, it is important to check the condensate pan and drain lines monthly throughout the air conditioning season.  Here’s how:

  1. Find the condensate pan – usually a metal or hard plastic pan about 3 inches deep – sitting below the HVAC’s air handling unit. In some cases, you may need to remove a metal panel to access it. The condensate pan should be nearly dry.  If it has significant rust all over, or is rusted out in sections, it must be replaced. Plus, signs of rust means there has been water backing up in the pan regularly, which is not a good sign.
  2. If the condensate pan has standing water in it or if there is water on the floor nearby, there is a problem with the condensation drain lines.  If your HVAC unit is in the attic, you might see water coming through the ceiling!  If this is the case, turn the HVAC unit off at the electrical switch and at the thermostat. Using rags or a wet/dry vacuum, remove all the water from the drip pan and around the unit.  Then clean the pan with a mild dish soap or 10% bleach solution.
  3. The drip pan connects to the condensate drain line, which carries water out of the home.  Locate where the drain line exits outside the house.  Be sure there are no obstructions, that the drain line is not buried under dirt or landscaping, and that you can see whether it is dripping.
  4. If no moisture is exiting outdoors even while the system is running or when the condensate pan is full of water, then the drain line is clogged. You may need to use a long, flexible rubber tube through the line – from each end – to dislodge the clog.  Another option is to connect the wet/dry vac to the outlet, and use your hands to make a “seal” around the drain line in order to draw the clog out, or use an AC drain sucker kit.
  5. With the system turned off, flush out the drain using distilled vinegar, hot water with mild dish soap, or a 10% bleach solution. Leave the solution to soak for up to 30 minutes, then rinse the lines with clean water. Be sure you can see the water exiting freely out of the exterior condensate line.
  6. Special cases: If the drain line does not have a direct downward slope allowing it to make use of gravity to help the water exit, you may need to have a small pump added to help push the water out.  If there is a reservoir which holds water until it exits, you may need to add a mild bleach solution, condensate drain line cleaner, or anti-algae tablets to the reservoir on a regular basis to prevent the growth of mold and algae. 

If you care about the quality of the air you and your family breathes every day – and want to prolong your HVAC investment – be sure to get your HVAC serviced regularly, and keep that condensation pan and drain clear! If you’re not comfortable with any of the steps listed above, call on Interstate AC service at (615) 832-8500. Rest assured, we’re here to help!

Posted on 06/15/2018 7:14 AM by Tony Anderson

Important Tips & Advice



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Did you know you should service your HVAC on a regular schedule – just like you would your car?  We have specialized maintenance programs to ensure the clean, energy efficient and safe operation of your HVAC systems.  This helps minimize service interruptions/breakdowns and maximize your equipment's lifespan.  All maintenance contract customers are assigned a primary technician that will get to know your facility and equipment and will treat it like his own.  You’ll receive discounts on repairs or new installations, and get priority service when it is cold or hot outside and you need service promptly.  Plus, maintenance contract customers are never charged overtime rates for emergency services after-hours, weekends or holidays. We’ll teach you how to save on maintenance costs by showing you things you can do yourself and when you need a technician. Here are some good posts:  Repair vs. Replace, Things to Try Before Calling for Service, Springtime Tips that Pay Off.


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