How to Clean or Un-Clog an Air Conditioning or Heat Pump Condensate Drain Line or Trap
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• How to clean or de-clog the air conditioning or heat pump condensate drain line - detailed procedures, products, methods
• Air conditioning condensate drain clogging - how to de-clog the A/C condensate line - how to fix a condensate drain stoppage
• A/C condensate drain line cleaning tools & products stop condensate drain line overflow: brushes, snakes, blow-outs, pumps, plumbing snakes or shop vacs all can be used to clear a condensate drain clog. But what is the quickest, simplest, least costly way to clear a blocked condensate line?
• How do I repair air conditioning condensate line water leaks?
• Questions & answers about how to un-block a clogged A/C or heat pump condensate drain

A/C or heat pump condensate drains can become clogged, leading to condensate leaks, spillage, or even bacterial hazards in a building.

Clogged air conditioner condensate drain lines can form another source of air conditioner or heat pump condensate leakage that can in turn lead to hidden water damage or in some locations an indoor mold problem or bacterial contamination.

Our photograph of a nearly full A/C condensate overflow pan (at left) shows what can happen if the primary condensate air conditioner condensate drain line is clogged and worse, the condensate drain overflow pan is also itself clogged and not draining properly. Luckily we caught this attic mold and bacterial pond before it had soaked the ceilings below.

We see air conditioner or heat pump condensate drain lines clogging for several reasons:

• Condensate trap debris dry-out cycle: Dust and debris or nearby insulation entering the condensate drain line trap near the air handler, often where the trap design includes a vertical standpipe open to the air, serving as an emergency overflow to prevent condensate from backing up inside the air handler itself. In months during which an air conditioning system is not in use, particularly for non-heat-pump systems that perform cooling-only, condensate and accumulated dust and debris that was resting in the condensate drain trap can convert to a dried plug of crud as the water portion of the condensate evaporates. After several years of this wet, sludge accumulation, and then drying cycle, the plug of dried sludge in a condensate trap or drain can actually block condensate flow through the system.
• Improperly-installed condensate drain lines with a long near-horizontal run can allow dust and debris to accumulate, dry, and ultimately block condensate flow in the drain line
• Insects, insect nests, or on larger piping systems, even rodents can clog a condensate drain line.
• Condensate overflow pan drain blockage: dust and debris also accumulate readily in a condensate overflow pan where it can flow to and block the opening to the overflow pan's independent condensate drain line. If a blockage occurs here, the condensate overflow pan may not do its job of preventing condensate spillage into the building. (Ref. Uniform Mechanical Code Sec. 1205 and Sec. 510. Condensate overflow pan is suggested for attic space per UMC (Uniform Mechanical Code) Section 1205.)

How do I Clean an Air Conditioning or Heat Pump Condensate Drain?

• Remove visible debris from the clogged air conditioning or heat pump condensate drain: start with a simple visual inspection. You may see a plug of crud blocking a condensate overflow pan right at its drain inlet - material that can be manually removed and the area wiped clean. Peering into the standpipe at a condensate drain trap, you may see crud right in that area that can be fished out or simply loosened and flushed through the drain line by working carefully so as not to break or loosen any pipe connections.
  
  Our photo (left) shows a poorly-installed A/C condensate drain system: the air handler condensate drain is installed in common with the overflow pan drain line - so that a blockage in the condensate drain line will guarantee that condensate spills onto the attic floor.
  
  The A/C condensate tray should have either had its own independent drain line, or it should have been installed with a sensor switch that shuts down the A/C or heat pump system if spillage is detected in the overflow pan. Finally, there is no trap on the condensate line and no air vent.

• Snake the clogged A/C condensate line carefully using a condensate drain brush or plastic tube: We've loosened and freed a clogged condensate drain line by simply snaking the line gently with a piece of plastic tubing inserted at the trap vent and pushed through the condensate trap.
  
  Remember that because condensate drain piping is usually 3/4" plastic piping you don't want to use unnecessary force that could result in breaking any pipe or causing a leak at a connection. Gently does the trick most of the time.
  
  Our photo (left) shows the trap at a condensate drain pipe right at the air handler. Notice those three red plastic caps? Each of those is an access port through which this air conditioning condensate trap and drain can be quickly and inexpensively cleaned.
  
  Notice that small black bristle brush clipped to the upper red cap in the center of our photo. The brush has a flexible blue plastic handle, allowing the homeowner or A/C heat pump service technician to easily push the brush through the trap and drain line to clean it.
  
  Because most A/C condensate drain clogs occur right at the trap, this is the quickest, easiest, lowest-cost method to clean and clear an A/C or heat pump condensate drain clog. Air conditioner / heat pump condensate traps with cleanout ports can be cleaned using soapy water and the manufacturer-provided cleaning brush. Some models can be easily disassembled for further cleaning of internal parts.
  
  Condensate traps that include cleanout caps include the EZT-150 EZ-Trap and UltraTrap (sketch at left) that work on both positive or negative pressure air handlers. Below we provide a link to installation instructions for the condensate drain trap provided by AirTech Products shown at left.
  
  
• Using a plumbing snake to clear a condensate line: In some cases a clog might occur in an A/C - heat pump condensate drain that is beyond the reach of your drain cleaning brush. Try a longer length of flexible plastic tubing as a gentle condensate drain snake, use a small plumbing drain snake, or try the remaining A/C condensate drain clog clearing methods listed below. For long condensate drain line runs, you may need to install additional cleanout ports in the line such as the EasyKlear cleanout port discussed just below.
• Using a CO₂ cartridge to blast out a clogged A/C or heat pump condensate drain line is a method followed by some service techs. Heating or air conditioning equipment suppliers sell a small CO₂ cartridge canister with an outlet adapter and fittings to connect to various sizes of piping. The canister is connected to the condensate drain line inlet (and the vent at the drain plugged with an expandable rubber plug sold for that purpose). A CO₂ cartridge is dropped into the canister and its cap screwed on. Screwing the canister top on tightly will puncture the CO₂ cartridge, sending a quick shot of high pressure gas through the drain line, clearing an obstruction. (This method is also widely used by oil heat service technicians to clear a clogged heating oil line.)
• Vacuum clean the clogged condensate drain line: Use a manual pump (such as the Mighty Pump) to vacuum clean a clogged air conditioning or heat pump condensate drain line. The pump inlet side is connected by an adapter fitting to the condensate drain line opening. You'll have to plug the nearby vertical standpipe at the condensate trap if one is provided. The manual condensate drain line pump's outlet side is connected to a hose run into a bucket or a nearby building drain to receive any waste.
  
  We like the clogged condensate drain vacuum cleaning approach better than the blow-out approach if we can get this method to work because it is more gentle, reducing the risk of damaged piping, and because we minimize the risk of blowing a plug of crud downstream to a more distant location where it can form a new clog or plug in a long condensate piping run.
  
  Several air conditioning and plumbing suppliers provide easy-to-clean air conditioning condensate cleanout ports such as the one shown above, including the Easy Klear condensate line cleanout (photo at left) that is particularly useful if your condensate drain line has a long run with a slope of less than 1/8" per foot. This A/C or heat pump condensate drain line cleanout is intended to be vacuumed using a connection to a shop vac.
• Blow out the clogged condensate drain line: Use a compressed air source or a manual pump such as the Mighty Pump (safer) to try blowing out the clogged air conditioning or heat pump condensate drain line and trap. Using a manual pump, the pump's outlet end is connected to the condensate drain opening or standpipe, any other nearby openings are plugged, and you use the pump to try to force the blockage through the system to an outlet. This approach works best if the condensate drain line is actually fully clogged and full of standing water or condensate.
  
  WATCH OUT: using high pressure to try to blow out a clogged drain pipe of any kind can result in damaging the drain piping, causing it to break or come disconnected, spilling ugly condensate and crud all over. This risk is greatest if the original piping connections were not properly glued or were not soundly made in the first place.
  
  
• Cleaning out partly-blocked, sluggish A/C or heat pump condensate lines: neither the vacuum method nor the blow-out method will work very well for cleaning a sluggish condensate line that is not totally blocked, since you may simply move air past the blockage rather than removing it. If you encounter this problem, try hooking up your pump in the "blow-out" configuration, then try filling the condensate line with tap water so that the pump pressure can act mechanically on the clog.

Thanks to reader Stuart Oakner for suggesting additional discussion of the Mighty Pump as a less costly way to clear blocked air conditioning or heat pump condensate drains than calling the HVAC service technician.

• The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ^® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.