Why Is My AC Dripping Water Inside? HK Guide (2026)

Updated 2026-05 · DrainFix HK 急通渠

Short answer: 95% of HK air-conditioner units that drip water inside the room have a clogged condensate drain, not a broken AC. Algae and dust build up in the flexible drain pipe — a HK humidity classic — and water that should drain to the outside backs up and drips inside instead.

This guide explains exactly what's happening, a 5-minute self-check you can do, and when it's worth calling a professional.

Why this happens (the physics)

An air-con unit pulls warm humid HK air over a cold evaporator coil. Moisture condenses on the coil and drips into a tray below it. From the tray, a small flexible pipe (the condensate drain) carries that water to the outside of the building.

When that pipe is blocked, the tray fills up. Once full, water spills out of the tray — and gravity takes it down through whatever path is available. That's the drip you see inside the room.

The 4 most common HK causes

1. Algae build-up in the flexible drain pipe (most common)

HK summer humidity is 80-95%. The constant warm wet inside of the drain pipe is a perfect environment for algae and slime to grow. Over a year or two, this gradually narrows the pipe until it's fully blocked. Symptom: water starts dripping after a heat wave, after the AC has been running flat-out for several days.

2. Dust and lint from a dirty filter

If your AC filter hasn't been cleaned in a long time, dust and lint blow past the filter, hit the cold coil, mix with condensation, and wash down into the drain — eventually clogging it from the AC side. Cleaning the filter doesn't unclog an already-clogged drain, but it stops the problem coming back.

3. Pipe slope is wrong (less common but worth checking)

Condensate drains rely on gravity. If the flexible pipe sags or runs uphill (sometimes after a renovation or after the AC was reinstalled), water pools in the low point, algae grows, and the pipe clogs. This is the kind of problem that recurs every 3-6 months even after clearing.

4. Outdoor pipe end blocked

The outside end of the drain pipe — sticking out of a wall or onto a balcony / light-well — can get blocked by debris, dust, paint over-spray (during HK building maintenance), or even insects. Easy to check from outside if you can see the pipe end.

5-minute self-check before calling anyone

1. Identify which AC unit is dripping. If you have multiple ACs, the problem is usually unit-specific.
2. Find the condensate drain pipe. It's usually a small white or transparent flexible pipe coming out of the bottom of the AC indoor unit. Trace it as far as you can — it will exit the wall or room.
3. Find the outside end. Usually visible on an exterior wall, light-well, or balcony. If you can see it, check whether water actually drips out when the AC is running.
4. Listen for gurgling. A partially-blocked drain often makes a quiet gurgle when water tries to flow past the blockage.
5. Check the AC tray. If you can safely access the indoor unit (don't force panels), see if the drip tray under the coil has standing water.

DIY options (and when not to)

Worth trying yourself:

• Clean the AC filter — won't fix the blockage but stops re-clogging.
• If you can reach the outdoor pipe end safely, gently clear visible debris (insects, leaves, dust).
• If the pipe end is accessible, you can try gentle suction with a wet-vac at the outdoor end. This works in maybe 30% of mild cases.

Don't try at home:

• Pouring chemicals down the indoor drain — most chemical drain cleaners can damage the AC's internal components or the flexible pipe.
• Disassembling the AC indoor unit — voids warranty on most HK units, and the panels are surprisingly tricky.
• Compressed-air blow-through from inside without proper sealing — can blow water into your AC's electronics.

When to call a professional

Call a drain professional (not a regular HVAC technician) if:

• Self-check shows no water coming out of the outdoor pipe end
• Drip is more than a few drops per hour during normal AC use
• Drip persists after filter cleaning
• You can't safely access the outdoor pipe end
• The drip is staining ceiling, wall, or wood flooring

What a professional will do (in our case: 10-15 minutes, HKD 250 fixed):

1. Compressed-air blow-through from outdoor end with proper seal at indoor end (clears 90% of cases)
2. Vinegar flush to kill remaining algae and prevent re-growth
3. Check pipe slope — re-route if water pools
4. Test by running AC 10 minutes; verify continuous outdoor drip and no indoor drip
5. Provide receipt

Why HKD 250 is the right HK price for this job

HK pricing varies wildly for AC condensate clearing. Some operators quote HKD 800-1,500. Here's what's actually involved:

• Travel: 20-30 min
• Setup: 5 min
• Clearing: 5-10 min
• Test + receipt: 5 min
• Total on-site: ~25 min

HKD 250 is a fair price that covers professional time and a written guarantee, without the inflated "specialist HVAC" pricing some vendors apply. We do drain work; AC condensate drains are drains. The HVAC inside the unit is somebody else's specialty.

Preventing this from happening again

1. Annual condensate flush. Have your drain pipe flushed once a year, before HK summer. We do this for HKD 200 if combined with another visit, HKD 250 standalone.
2. Clean AC filters every 4-6 weeks during summer. Reduces dust load on the drain.
3. Check the outdoor pipe end every 2-3 months. Make sure debris isn't accumulating.
4. Don't ignore early gurgling. A drain that gurgles is a drain that's about to fully clog. Get it cleared while it's still partial.