How to Unclog an AC Drain Line/Pipe

A clogged air conditioner condensate drain line is a very common problem. In this article we’ll discuss the most common symptoms of a clogged AC drain line – and how you can fix it.

Air Conditioner Drain Line Location: Where is My Condensate Drain Line?

The AC drain line location is wherever your air handler is located and in most residential installs the condensate would be made of either PVC or CPVC.

A commercial install may use copper drain lines instead.

Air Conditioner Drain Line Outside the House

In the majority of AC installations, your condensate drain line will be located outside the house where your air conditioning unit is located.

Once you locate the condensate drain outside of the home, you can then work to fix the clogged pipe.

Condensate Drain Line Located Elsewhere

Sometimes, the drain line is not located outside of the house. A few places this might have been installed are:

  • The attic!
  • The garage
  • The basement
  • A cupboard or closet

What Causes a Clogged AC Drain Line?

The majority of clogged AC drain pipes are because of a build up of algae and mold.

When the warm air is brought into the unit and it goes across the evaporate coil, this created condensate.

Algae can then grow inside the drain piping, which can get very humid and provide the perfect conditions for algae to thrive and grow.

A general rule of thumb is that the more you use the AC unit, the more they will get clogged. This is because while the unit is running, the condensate is constantly flowing through the piping.

If the AC is installed in a humid environment, this can obviously make the problem even more common, and clogs can happen regularly.

Other common issues which can clog the drain line are:

  • Rodent and insect infestation
  • Dust, dirt, or debris inside the drain line
  • Corrosion or rusting

AC Drain Line Clogged Symptoms

  • Standing/flooding water - The evaporator unit removes the moisture and humidity from the air, and this can cause a build up of water around the air handler, which drips into the secondary pan.
    • Most AC units need a water safety switch which prevents flooding if the condensate drain line is clogged up.
    • Water build up and flooding could also indicate a problem with frozen coils, a cracked drain pan, or a poorly installed AC unit.
  • The AC won't cool or run - A clogged drain line can stop the AC from running or cooling, and this is usually because it trips the water safety switch.
    • If the safety switch is hooked to break the Y wire, it will shut down the AC compressor
    • If the safety switch is hooked to break the R wire, it will break the air handler low voltage
  • Wet walls - Check the walls close to the indoor AC unit. Moisture which doesn't drain can seep into the walls and make them damp, which a common symptom of a clogged condensate drain line.
  • Mold in the drip pan - The drip pan should be dry because in a functioning AC unit the water would get emptied by the drain line. Water that doesn't drain means that mold can grow because of the darkness and humidity inside the unit
    • The accumulation of water might also indicate that the condensation pump is faulty
    • If there is mold inside the AC unit, another symptom would be the musty, mold smell

How to Unclog Your Air Conditioner Drain Line

Here are some commonly used tips for cleaning our your AC drain line to unclog it:

  • Use a drain cleaning brush and hot water - for air handlers that have the drain clean out cap and a vent, this might be all you need to unclog it.
  • Hot water and a wet vacuum - with this method you would connect the wet vac to the end of the drain line and turn it on. Next, pour hot water down the drain line from the air handler and the wet vacuum should suck the clog right out of the line.
  • Use compressed air - a small air compressor can be an invaluable HVAC tool and depending on the level of blockage it could be used to clear the condensate line.
  • Use a proper cleaning tool - if your line is clogged at the trap you should be able to push it straight through with a drain cleaning brush. For clogs further down the line, you could use a small hand snake, as long as you pick one that can handle 90 degree bends.

How Can I Prevent My Drain Line Getting Clogged?

There's no 100% guaranteed way to prevent your AC drain line from getting clogged up.

Making sure you take good care of the unit and maintain it with regular servicing and cleaning of the air handles, the drain line, the pans etc will go a long way.

I would also recommend getting a small wet vacuum and running the drain line unclogging I mentioned above a couple of times a year. If you don't wait until the line is so backed up that it breaks the unit, it's much easier to keep it clean.

I've also had some luck with algae tablets which are made specifically to prevent algae from having a free run at your drain line.

You basically pop a couple of these tabs into the drain pan a few times a year, and then prevent algae growth.

These tablets should be used in addition to regularly cleaning and maintenance though, as in my experience they will never completely eliminate the problem. One thing they do prevent is the foul smells coming out of the air handler!

The final tip is that if you don't want to be unclogging the AC condensate drain line yourself, you should find a local HVAC company and sign up for some kind of maintenance plan - which includes condensate drain cleaning.

The peace of mind and ease of having this maintenance plan is very often worth the cost, and you'll never have to get your hands dirty in the drain line again.