AC condensate drain line is clogged

Symptoms

• Water backing up near the indoor unit
• AC shuts off unexpectedly, especially on systems with a safety float switch
• Slow or no dripping at the drain line's outside exit point

Likely causes

• CommonAlgae or sediment buildup inside the drain lineCondensate provides a damp environment where algae and slime readily grow and narrow the tube.
• PossibleKinked or improperly sloped drain tubingA line that doesn't slope downward properly can trap water and clog easily.
• PossibleClogged condensate pump (in basement installations)Pumps can jam or fail, backing water up into the system's safety switch.

What to do

1. Turn the AC off before working on the drain line.
2. Locate the condensate drain line, usually PVC tubing running from the indoor unit to a floor drain or outside wall.
3. At the outside or floor drain end, use a wet/dry shop vac to pull any clog free.
4. Alternatively, disconnect the line at the indoor unit over a bucket and flush it with water and a small amount of vinegar.
5. If there's a condensate pump, check its float switch moves freely and the pump runs when the reservoir fills.
6. Reconnect the line, restart the AC, and confirm water flows freely from the outside end during the next cooling cycle.

Tools and parts

• Wet/dry shop vac
• White vinegar
• Bucket

When to call a pro

Call an HVAC technician if the line clogs repeatedly, the condensate pump has failed, or you're not comfortable disconnecting the tubing.

Safety