R-Pro › Field cases › Air conditioning
Indoor Unit Outlet Condensation → Ceiling Stains
Likely causes
Indoor relative humidity too high — dew point rises above RH 70%
Check: Measure indoor RH with digital hygrometer — if ≥70%, conditions are met for condensation on cold outlet metal. Compare setpoint temperature with indoor dew point
What to do: Raise setpoint to 22°C+ to check short-term condensation clearance → for high-humidity environment, improve ventilation or recommend separate dehumidifier → target indoor RH below 60%
Insulation foam inside outlet casing aged or peeled → cold bridge created
Check: Inspect insulation foam inside indoor unit outlet casing — visually check for peeling, shrinkage, missing sections. Confirm if condensation is concentrated on specific areas of the casing
What to do: Remove all insulation foam inside casing → re-attach expanded polyethylene (PE foam) ≥3 mm thick using adhesive + double-sided tape → ensure no gaps at seams
Refrigerant overcharge — liquid refrigerant return causes sharp evaporator temperature drop
Check: Check SST with low-side gauge — R-410A 0.5 MPa ≈ 0°C; below this suspects overcooling. Measure superheat — below 5–8 K indicates overcharge or expansion valve wide open
What to do: Recover excess refrigerant until superheat reaches 5–8 K → after adjustment, verify outlet condensation is eliminated
When condensation is suspected, measure outlet surface temperature with digital thermometer — below indoor dew point confirms condensation. Do not touch the surface.
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