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Identifying A Restricted AC Drain Line

The AC drain lines in your HVAC system play an important role in the cooling process. If they have collected buildup or otherwise become restricted, your system will not function properly and may even leak and overflow.

How do AC Drain Lines Become Restricted?

During the cooling process, the drain lines in your AC system are used to collect and dispell runoff water and cooling refrigerant from your system. With all of that runoff running through the pipes, dirt, algae, mildew, and other forms of buildup can collect inside. Eventually, it can clog the line and restrict any water from flowing through.

How to check for clogged drain lines

  • Locate the drain pan. It’s often under the indoor coil in the air handler or in a small cabinet next to the air handler. If the drain pan is full of water, the AC drain lines are likely clogged.


    CAUTION: Turn power off to any piece of equipment that you'll be examining.

  • Find the AC drain line. It's usually made of white PVC pipe, begins at the indoor HVAC unit and may terminate outside.

  • Place a bucket at the end of the line and check to see if it fills up with water. If no water collects in the bucket, you likely have a clog.

  • Locate the small vertical section of the pipe, called a PVC cleanout tee, and remove the cap. Slowly pour water down the drain (a gallon will do). If the water backs up, the drain line is clogged.

  • Check the entire drain line for proper slope: 1/4" per foot of pipe run downhill from the indoor HVAC unit. If there is a u-shaped trap there should be a T fitting that serves as a cleanout. Make sure that trap is not clogged.

If these steps didn't help you nail down the issue, consider other causes of ac water leaks.

What To Do If Your AC Drain Lines are Restricted?

In order to fix the issue, you will need to clear the AC drain lines of all that buildup. First, empty the drain pan (if it has filled up with water), and then unclog the drain line using a wet/dry vacuum or a pressure washer.

Didn't work? If your AC drain lines are still clogged up, you've probably got a pretty tough clog on your hands that requires professional tools. You can reach out to our Remote Assist expert for a free virtual diagnosis!

NOTE: This content is for informational purposes only, and HomeX and its affiliates disclaim all liability related to it. If you decide to perform any tasks based on this information, you assume all risks, including the risk of loss or damage to property or personal injury.

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