Condensate drain
The path that carries water from the drain pan out of the building, by gravity or with a pump. If the path is obstructed or a pump stops, water collects in the pan instead of leaving the building. Many systems include a float switch that halts operation before the pan overflows.
Also called drain line, condensate pump, drain pan
What is the condensate drain?
The condensate drain is the route water takes from the drain pan under the coil to the outside. It runs by gravity where the fall allows, and by a small pump where it does not.
Condensate drain: how it works
Water condensing on the cold coil runs into a pan and leaves through a hose or pipe. Gravity systems rely on continuous fall and a trap that stops air being drawn back up the pipe. Where the unit sits below the discharge point, a small pump lifts the water instead, and that pump has its own float and its own failure modes.
Where you meet the term
- In a water leak from an indoor head, where the drain path rather than the refrigerant circuit is the first thing checked.
- In a system that runs in fan mode but will not cool, where a float switch has cut the cooling call.
- In annual maintenance, where the pan, trap, and drain line are cleared before the cooling season.
How to check it
- Find where the drain hose discharges outside. A cooling system in humid weather should discharge a steady trickle. Nothing coming out while the unit cools points at an obstruction upstream. Owner check
- Check that the hose has continuous fall and no kinks. A hose that rises, loops, or is pinched behind furniture holds water back into the pan. The visible run is owner-checkable. Owner check
- Clear the pan and line properly. Opening the indoor unit to reach the pan, and flushing or vacuuming the line, is technician work on most wall-mounted heads. Technician
Condensate drain: what it is not
- Water from an indoor unit is not a refrigerant leak. Refrigerant leaves as gas; the liquid you see is condensate.
- A pump that hums is not necessarily working. It can run without moving water if the impeller is fouled or the discharge is blocked.
Condensate drain questions
How much water should a mini-split produce?
Enough to be a steady drip or trickle at the outside discharge in humid weather, and little in dry conditions. The amount tracks how much moisture the air holds, not how hard the unit is working.
Why does my system cool for an hour then stop?
One explanation is a drain that cannot keep up, letting the pan fill until a float switch cuts the cooling call. The fan can keep running, which makes the symptom resemble a control fault.
Can I pour anything down the drain line to clear it?
Products exist, but manufacturers specify what may be used with their pans and materials. Using the wrong one can damage the pan or the pump, so check the manual before pouring anything in.
Where this definition comes from
Written from manufacturer support article material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- Why Is My Mini-Split Leaking Water?General ductless condensate and drainage guidance from Gree.
- Why Is My Mini Split Leaking Water?Trane ductless condensate, drain, filter, frozen coil, drain pan, and installation leak guidance.