Install the Condensate Drain

Slope the line, set a correct-depth P-trap for the draw-through coil, add primary + secondary drainage and a float switch wired to cut cooling, then flush and test.

Approx. 75 min

Before you start

•Know the cabinet's static pressure (negative on a draw-through coil) so the trap is deep enough to seal against it and still drain.
•Drain termination point and a legal route identified (to a sanitary drain, condensate pump, or approved exterior point — never to a place that backs up).
•Secondary drainage path available: a secondary drain pan under the unit or an auxiliary (secondary) drain port, per code for attic/above-ceiling installs.

Tools & materials

PVC pipe, primer + cement, P-trap and cleanout/test tee fittings · Pre-built condensate trap or fittings to build one · Float safety switch(es) (in-line trap + secondary pan) · Level / torpedo level · Bucket of water (or a jug) to flush and test

View

0% complete

Primary drain & slope

Pitch the primary line for gravity drainage
Run the primary condensate line with continuous downhill slope from the coil pan to the termination. No bellies, no uphill runs — water that pools airlocks the line and backs up into the pan.
Tools: Level
Target: Slope ≥ 1/8 in per foot continuously downhill; no low spots/bellies
Install a correct-depth P-trap for the draw-through coil
A draw-through (most residential) coil sits in negative pressure, so the blower would suck air up the open drain and HOLD water in the pan unless the trap seal is deeper than the cabinet's negative static. Size the trap depth to the static and add a cleanout/test tee. A trap that is too shallow won't drain; one with no vent downstream can siphon dry.
Target: Trap seal depth > cabinet negative static (rule of thumb: inlet leg ≈ static + ~1 in, outlet leg deeper); add a cleanout
⚠ Don't omit the trap on a draw-through coil — the pan overflows even though the line looks 'open'.

Secondary drainage

Provide a secondary/auxiliary drain or pan
For units over a finished space (attic/above-ceiling), provide secondary protection: either pipe the coil's secondary (auxiliary) drain port to a conspicuous location, or set the unit in an emergency drain pan with its own drain — so a clogged primary is caught before it floods the ceiling.
Target: Secondary drain to a conspicuous point OR a separate drain pan with independent drain, per code for the location

Float safety switch

Wire a float switch to cut cooling on backup
Install a float switch wired in SERIES with the Y / 24V cooling circuit so a backup shuts off the compressor before water overflows. Best practice is two: one in the primary trap (or coil pan) and one in the secondary drain pan as the last line of defense.
Target: Float switch(es) break the Y/24V cooling call on high water; primary trap + secondary pan covered
⚠ Land the switch so it interrupts cooling (not the whole 24V) — opening R can disable safeties or heat unexpectedly; follow the switch's wiring guide.

Flush & test

Flush and water-test the whole drain
Pour water into the pan/test tee and confirm it runs out the termination with the trap holding a seal and no leaks at the joints. Then raise each float by hand (or fill the pan) and confirm the cooling call actually drops out.
Target: Water drains freely, trap stays sealed, no joint leaks; tripping each float stops the compressor