Learn how to clean an AC drain line – to keep your unit in top condition

Learn how to clean your AC drain line so that it can perform to its optimum during the warmer weather.

living area with large window and air conditioning unit
(Image credit: Getty images)

Maintaining your air conditioning system goes beyond changing filters and adjusting thermostats. One crucial yet often overlooked aspect is cleaning the AC drain lines. Cleaning your HVAC unit is crucial for maintaining your system's efficiency and should be maintained correctly. 

Over time, your air conditioning drain line can clog with algae, dirt, and debris. This can cause water damage in your home and prevent your air conditioner from functioning correctly, creating a bad smell. Clean your drain line regularly to maintain your air conditioner’s health and prevent your AC unit leaking water, causing damage to your home.

Neglecting this task can lead to costly repairs and decreased system efficiency. In this guide, we'll walk you through the process of cleaning AC drain lines step-by-step, providing expert advice to ensure your HVAC system drains smoothly.

How to clean an AC drain line 

Cleaning your drain line is a relatively simple DIY task that saves money and keeps your AC running smoothly. Here's a detailed step-by-step process to get you started: 

Air con

(Image credit: GettyImages)

1. Turn the power off and check the pump

Whenever you’re working on any appliance in the home, especially your air conditioner, be sure that the power is off by switching off the breaker. A simple circuit breaker lock from Amazon will ensure that a well-meaning family member doesn’t turn the power back on while you’re working.

‘If your system has a condensate pump, your first step should be to ensure that this pump is working properly,’ says Mason Duckett, HVAC expert. ‘If it’s not, you can cause water damage to your home by clearing this line. To check the pump, pour a small amount of water into its reservoir and see if the water is pumped out.’  

If so, you’re good to move on to the next step. If it does not, you’ll need to look into repairing or replacing the pump before moving forward. A malfunctioning pump can cause a flood in your home.

Mason Duckett
Mason Duckett

Mason Duckett is Tonna Mechanical’s Lead Comfort Specialist. Since 1976, Tonna Mechanical has continually provided the finest and most trusted HVAC, plumbing, air quality, and water treatment services in Southeast Minnesota. 

2. Find and Inspect the Drain Line

The AC drain line usually exits near the outdoor unit. This is often a white PVC pipe that runs from your indoor air handler to the exterior of your home.

Before you begin flushing your line, inspect the opening to make sure there’s no visible damage or clog in the line.

3. Vacuum and flush

Attach a wet/dry vacuum to the end of the AC drain line where you previously located it outside your home. Use a rag or some XUXU Heavy Duty Waterproof Black Duct Tape from Amazon to create a tight seal where you attach the vacuum to the drain line. Run the vacuum for roughly one minute to clear any blockages in the line.

After you’ve vacuumed the line for about a minute, you can then flush the line. White vinegar will kill any mold or algae inside the pipe. You’ll need to close the drain line (duct tape should work for this) so that the vinegar doesn’t just run out of the line. Pour about one cup of vinegar in at the access point of the line, which is normally close to the indoor air handler, where the condensation originates.

Leave the vinegar in the line for roughly 30 minutes in order to break down any lingering residue.

4. Open the drain line and reflush

Once you’ve let the vinegar sit, open the drain line again. This is a very important step to prevent water damage to your home.

Next, flush the line with water to wash out any debris. Start with small amounts of water and ensure that the water is draining outside the home. It can be helpful to have another person with you who can confirm that the water is draining properly as you pour it into the line. 

If you’re confident that there’s no clog in the drain line, you can increase the amount of water you flush through the line. When the water flows smoothly and clearly from the drain line, you can stop flushing the line.

5. Check the drain pan & turn the power back on

‘While you're in the area, now is a good time to also check the drain pan located under the indoor air handler,’ says Josh Mitchell, HVAC technician and owner of Air Conditioner Lab.  ‘If you find water or sludge in the drain pan, clean it with soap and water to avoid rust and deterioration.’

Josh suggests that you may want to consult with an HVAC technician to look into why water and sludge are accumulating in the pan. Finally, you can remove your circuit breaker lock and turn the power back on to your unit.

Josh Mitchell
Josh Mitchell

Josh Mitchell is a plumbing expert and HVAC technician and the owner of Air Conditioner Lab and Plumbing Lab. 


What causes an AC drain line to keep clogging?

One of the main causes of blocked AC drain lines are leaves and other yard debris. Another reason could be condensation. Condensation can occur when the evaporator coils stay wet as it removes the moisture out of the incoming air.  

For tougher blockages, you can use a special pressurized flush that pushes water through the system to clear out build-up. This is typically a method used by HVAC professionals due the equipment required but can be achieved at home.

Cleaning your AC drain line is a straightforward process that can prevent many common air conditioning problems. Keeping this line clear helps ensure that your system operates efficiently and avoids issues related to excessive moisture.

Seraphina Di Mizzurati
Contributing Editor

Seraphina is a contributing editor at Homes & Gardens, writing Solved features on organizing and storage. She loves to decorate and also grow her own produce from her home in London. Her previous experience includes working at Women's Health and Fabulous Magazine.