R-Pro › Field cases › Air conditioning
Outdoor Unit PCB Short Circuit from Moisture Ingress — Rainwater Entry, Damaged Waterproof Cover
Likely causes
Cracked or missing waterproof top panel — rainwater falls directly onto PCB
Check: Visually inspect outdoor unit top panel — check for cracks, warping, missing sections. Check PCB surface for burn marks (brown/black traces), verdigris (green), moisture stains
What to do: Dry PCB before powering — compressed air or oven at 60°C for 30 min. If burn marks present, decide to replace → repair or replace waterproof cover with silicone sealant (verify IP44+) → re-seal cable entries with neutral silicone, cure 24 h
Blocked drain hole → condensate pools inside → PCB lower section submerged
Check: Locate 4 drain holes at outdoor unit base — check for blockage by debris (dust, leaves, cobwebs). Confirm whether moisture pools on unit interior floor
What to do: Clean drain holes — remove debris, confirm clear with compressed air → after PCB replacement, apply conformal coating spray for moisture protection to prevent recurrence
Cable entry sealant hardened or missing → moisture ingress via capillary action
Check: Check silicone condition at cable/pipe entry holes — look for cracks, shrinkage, missing sealant. If hard when pressed with finger, replacement needed
What to do: Fully remove existing sealant → fill with neutral (non-acid) electrical-grade silicone → cure 24 h before powering
Never power a wet PCB — it causes secondary burnout of otherwise good components. Always dry and verify before energizing.
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