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How to Clear an AC Drain Line with a CO2 Drain Gun (The 5-Minute Method)

May 26, 2026

How to Clear an AC Drain Line with a CO2 Drain Gun (The 5-Minute Method)

A clogged condensate line is the most common reason an AC system shuts down or leaks water into the house. The fastest, cleanest fix is a CO2 drain gun — the same tool service techs carry. Here’s exactly how to do it.

What you need

Step by step

  1. Kill power to the air handler. Flip the breaker or the service switch. You don’t want the unit cycling while you work.
  2. Find the condensate line. It’s the PVC pipe (usually 3/4”) leaving the indoor unit’s drain pan. Look for the cleanout tee — a vertical stub with a cap near the unit.
  3. Disconnect or open the cleanout. Unscrew the cap. If there’s standing water in the pan, towel it up now.
  4. Load the drain gun. Screw a 16g threaded cartridge into the gun until it seats against the gasket. Don’t pre-puncture — the trigger does that.
  5. Seal the gun against the line. Press the rubber nozzle firmly into the cleanout opening, pointed away from the unit (toward the outdoor termination).
  6. Fire one short blast. One trigger pull sends ~800 PSI of CO2 down the line and blows the algae plug out the far end. You’ll usually hear it.
  7. Verify flow. Pour a cup of water into the cleanout — it should drain freely. If it backs up, fire a second shot.
  8. Re-cap, restore power, done.

Why CO2 beats a shop vac

A wet/dry vac pulls from the outside termination and only works if you get a perfect seal — awkward under Minnesota decks in July. A CO2 blast pushes the clog out with far more force, takes one person, and weighs nothing on the truck. At roughly $0.70 per cartridge in bulk, it’s also cheaper than the gas to drive back for a callback.

How often should drain lines be cleared?

Once a season for most homes; twice in humid climates or homes with the air handler in the attic. Many techs fire a preventive shot during every spring tune-up — it takes thirty seconds and prevents the #1 summer emergency call.

FAQ

Will the CO2 blast damage PVC fittings? No — a short blast through an open line is well within PVC tolerances. Don’t fire into a fully capped, blocked line with no outlet.

What size cartridge do drain guns take? Almost all use 16g threaded (3/8”-24). Heavy-duty guns also accept 45g threaded for long runs.

Can homeowners do this or is it tech-only? It’s homeowner-friendly — the gun is point-and-shoot. Respect the basics: power off, eye protection, never point at a person.

Outfitting a crew? We supply 16g threaded CO2 by the 100-count case with free fast shipping from Minnesota — or get wholesale pricing.