To unclog an AC drain line: turn off the system, find the PVC cleanout tee near the indoor unit, remove the cap, clear the blockage with a wet/dry vacuum at the outdoor end of the line, then flush with distilled vinegar. In Tampa Bay’s humidity your AC can pull 10–20 gallons of water a day out of the air, and the warm, algae-friendly drain line that carries it away is one of Florida’s most common AC service calls. Most clogs are a 30-minute DIY job — here’s exactly how.
How to know your drain line is clogged
- Water pooling around the indoor air handler or stains on the ceiling below it
- The AC shuts off and won’t restart — a float switch has tripped to prevent overflow
- A full or overflowing drip pan under the indoor unit
- Musty smell near the air handler
- No water dripping from the outdoor drain outlet on a humid day when the AC is running (it should drip steadily)
What you’ll need
- Wet/dry shop vacuum with a hose
- Duct tape or a rag (to seal the vacuum hose to the drain pipe)
- Distilled white vinegar (about one cup)
- A funnel, towels, and a flashlight
The 6 steps
- Turn off the AC at the thermostat AND the breaker. You’ll be working around the drain pan and electrical components.
- Find the drain line. It’s a white 3/4-inch PVC pipe leaving the indoor air handler (garage, closet, or attic), with a T-shaped cleanout fitting and cap near the unit. Follow it to where it exits outside, usually near the condenser.
- Check the drip pan. If the pan under the indoor coil is full, soak up the water with towels or a wet/dry vac — a full pan means the clog is real and the float switch has likely tripped.
- Vacuum the outdoor end. Take the wet/dry vac to the drain outlet outside, seal the vacuum hose around the pipe with duct tape or a rag, and run it for 2–3 minutes. You’re pulling the algae plug through the pipe the same direction the water flows. Check the vacuum canister — a successful pull usually shows sludge and a slimy algae plug.
- Flush with vinegar. Back inside, open the cleanout cap and slowly pour about a cup of distilled vinegar down the line (a funnel helps). Let it sit 30 minutes to kill remaining algae, then follow with water to confirm it flows freely to the outside outlet.
- Restore power and watch. Cap the cleanout, turn the system back on, and check the outdoor outlet for steady dripping over the next few hours. If the float switch had tripped, drainage restores normal operation.
Keep it from clogging again
- Pour a cup of distilled vinegar down the cleanout every 1–3 months during cooling season (skip bleach — it’s harsh on PVC glue joints and drain pan coatings).
- Change your air filter on schedule; dust that reaches the wet coil becomes drain line sludge.
- Ask for a drain line flush and pan treatment at your annual maintenance visit — it’s standard in a good tune-up.
- If your system doesn’t have a float switch (overflow shutoff), have one installed; it’s cheap insurance against ceiling damage.
When to call a pro instead
Call for service if the vacuum trick doesn’t restore flow (the clog may be deep in a long or poorly-sloped run), if water has already damaged drywall or flooring, if the line clogs repeatedly despite monthly vinegar, or if the drain pan itself is rusted or cracked. Repeated clogs sometimes mean the line was run with too little slope — a permanent fix a technician can re-plumb in one visit.
Frequently Asked Questions
Can I pour bleach down my AC drain line?
Vinegar is the better choice. Bleach can degrade PVC cement joints and corrode the drain pan’s metal parts, and its fumes are rough in a closed air handler closet. Distilled vinegar kills the same algae safely.
How often should I clean my AC drain line?
Flush with vinegar every 1–3 months during Florida’s cooling season, plus a professional flush at your annual maintenance visit.
Why does my AC shut off when the drain line clogs?
A float switch in the drain pan senses rising water and cuts power to prevent an overflow through your ceiling. Once the line is cleared and the pan drains, the system can run again.
How much does professional drain line cleaning cost?
Typically $75–$250 on its own, and it’s commonly included in a maintenance plan visit. Compare that to the cost of a water-stained ceiling — prevention wins.
Where does the AC drain line go?
From the indoor evaporator coil’s drain pan, through a 3/4-inch PVC pipe, to the outdoors — usually exiting near your outdoor unit or a flower bed. On a humid day it should drip steadily while the AC runs.
Clog won’t clear — or water’s already where it shouldn’t be?
Pronto Service Pros is a family-owned HVAC company serving Tampa, St. Petersburg, Clearwater, Brandon, Wesley Chapel, Spring Hill, Bradenton, and communities across Hillsborough, Pinellas, Pasco, Hernando, and Manatee counties. If your drain line keeps clogging or the float switch keeps shutting your AC down, our licensed technicians can diagnose and fix it fast — often the same day. Call (813) 341-5400 or book online for a free estimate, and ask about Club Pronto membership for priority service and maintenance discounts.