How to Unclog AC Drain Line in Attic in 8 Steps

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Last updated: 
June 26, 2018

The A/C condensation drain line, which is usually either a 1/2" or 3'4" PVC pipe that extends from the attic to an outside wall near the condenser, enables water and moisture to exit the A/C unit during the refrigeration process. It is typically characterized by a slow drip when the A/C is in use.

However, due to its function, location, and dark, cold environment, it can also become a breeding ground for algae as well as bug and critter nests, which over time can cause blockage in the drain line and an overflow in the drain pan, which can leak and damage drywall in the ceiling.

One telltale sign that your A/C drain line is clogged is that the fan on the outside unit may continue to spin, but you may not be getting much air from your unit. In which case, you can use the following tips on how to unclog ac drain line in attic to see if it helps.

how to unclog ac drain line in attic

Tools for the Job

  • A small funnel for pouring liquids.
  • 1/2 of gallon bleach for flushing and disinfecting.
  • A shop vacuum for removing clogs.
  • A thermometer (optional), for recording A/C temperatures.

Step 1: Turn off the A/C Unit

As a safety precaution, always shut off power to the A/C unit before making adjustments or repairs.

Step 2: Locate the Main Drain Line in the Attic

In the attic, locate the main drain line. It is near the blower motor and usually just below the secondary drain line. Many drain pans have a secondary drain pipe that enables water to exit the system to the outside, usually by way of a second drain pipe located on the upper outer wall, to protect against drain overflow.

Furthermore, since the secondary drain line only kicks in when the main drain is clogged, it's also another telltale sign that the main drain is clogged when precipitation is exiting from the secondary drain pipe located on the outside wall.

Step 3: Remove the Cap on the Main Drain Line

Remove the removable cap or plug on the main drain pipe. It is usually located at the top of the drain line. Or, it may be located further down the pipeline on a threaded tee.

Step 4: Place a Funnel into the Main Drain Pipe

Next, insert a small funnel into the main drain pipe to prepare it for flushing and cleaning. The funnel will help prevent spillage as the disinfectant is poured down the pipe.

Step 5: Flush the Main Drain Pipe

With the funnel securely positioned into the drain pipe, slowly pour a half gallon of regular household bleach down the drain.

The bleach itself will kill any existing algae, while the odor will help freshen the pipe as well as deter unwanted bugs and critters from making their home in the pipes. This is especially useful during colder seasons when the unit is not in use.

For a chemical-free alternative, you could simply use white vinegar. However, though vinegar is effective at killing algae, it may take longer to remove clogs. Simply pour six ounces of white vinegar slowly down the drain. Repeat every few months to keep the drain clear.

Step 6: Use a Shop Vacuum

Once you have flushed the drain from the attic, next, place a shop vacuum over the outside drain hole to suction out any blockages. Or, you could simply run a fish or wire clothes hanger down the drain to help clear the blockage.

Step 7: Repeat Steps 5 & 6 as Needed

For how to unclog ac drain line in attic involving more stubborn clogs and buildup, you may need to repeat steps 5 & 6 a few times to clear the pipe. Repeat the process until the main drain line is clear and water no longer trickles from the secondary drain line.

Step 8: Turn the A/C Back On

Place the cap back on the main drain line, and then turn the A/C back on. You should notice that the fan inside the outdoor unit is spinning and air is now coming out. You should also notice water exiting the main drain line in a steady drip.

Allow the A/C to run for about 15 minutes on the desired temperature setting. Afterward, if you'd like, simply check for accurate temperature with a thermometer.

To record the temperature output, simply point the thermometer at the supply register closest to the inside A/C unit; it will give you a digital temperature reading. If the temperature is off, it may be time for an A/C tune-up.

Caution Notes

When incorporating these tips on how to unclog ac drain line in attic, be sure to follow the manufacturer's safety recommendations to avoid damaging your system.

When working with chlorine bleach, it is also a good idea to wear protective clothing. Use a plastic apron, eyewear, rubber gloves, and maybe even a face mask to avoid damaging your clothes, irritating your skin, and breathing in harmful fumes.

Final Thoughts

Keeping your A/C drain line clear is imperative for an efficient working system to help keep your home cool and also avoid damaging your ceiling, which can cave during drain pan overflow and lead to costly repairs. To keep your A/C drain clear, it is recommended that you use these tips on how to unclog ac drain line in attic at least once a year.

If only your social media friends also knew they could keep their A/C running efficiently this summer and their ceiling intact with these tips on how to unclog ac drain line in attic. After trying these tips on how to unclog ac drain line in attic, be sure to inform us of your experience.

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