R-Pro › Field cases › Air conditioning
Drain Clog — Condensate Overflow / Indoor Unit Leak
Likely causes
Slime, algae, debris buildup in drain line — most common cause
Check: No water flowing from drain exit = clogged. Look into indoor unit drain pan — if water is high with dark/sticky color, slime. Touch outer drain tip; slimy texture confirms. Partial clog overflows after 1–2 hours of operation.
What to do: 1) Vacuum drain end with wet/dry shop vacuum — slime gets sucked out whole. 2) If insufficient, blow compressed air in reverse direction (from drain pan side). 3) Regular drain-cleaning tablets (mild chemical). 4) Schedule annual cleaning — semi-annual for restaurants and high-humidity environments.
External drain outlet blocked, frozen, or insect nest
Check: Visually and physically inspect external drain tip — spider webs, wasp nests, animal carcasses. Below 0°C winter, freezing possible. If exit is buried in soil or in flower pot, natural blockage.
What to do: 1) Clear blockage and protect drain exit — install insect screen, raise exit above soil/pot. 2) Freeze protection: insulate drain line, add electric tracing cable in cold climates. 3) Drain tip must be ≥30 cm below indoor unit position for gravity flow. 4) Inspect drain exit during regular service.
Missing or clogged P-trap — negative pressure prevents drainage
Check: On DX (direct expansion) systems, blower creates negative suction-side pressure that pulls back drain water — P-trap required. If no drainage during operation but flows suddenly on shutdown = no P-trap. P-trap itself clogged stops flow.
What to do: 1) Install P-trap if missing — trap depth ≥ 1.5× blower static pressure (typically 5–10 cm). 2) Disassemble and clean clogged trap. 3) Some traps have cleanout plugs for service. 4) Auto-traps are available for trapless systems — block automatically under negative pressure.
Drain clogs are the #1 most common service call. Slime is 90%; external blockage, freezing, and missing P-trap account for the rest. Standard toolkit: wet/dry vac + compressed air + cleaning tablets.
All 565 cases work offline in R-Pro, with error codes for 62 brands and P-T data for 108 refrigerants.
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