Drain Pan Heater Not Working → Drain Line Ice Blockage

Question

Accepted Answer

Drain pan heater open-circuit → defrost water refreezes before draining, ice accumulates under pan. Check: Measure heater resistance: ~484Ω for 100W, ~242Ω for 200W (at 220V). ∞ = open circuit What to do: Replace with same-wattage heater → apply power alone and verify surface temperature rises within 10 seconds Defrost timing error — cooling restarts before drain heater activates, defrost water refreezes immediately. Check: Check sequence diagram: drain heater should pre-activate 5 min before defrost start and remain on ≥10 min after defrost before cooling restarts What to do: Modify controller sequence settings: drain heater pre-delay +5 min and post-delay +10 min → monitor one full cycle to verify Drain pipe insufficient slope (<1/50) — pooled water freezes even with heater running. Check: Measure drain pipe slope with level — verify ≥20mm drop per 1m (approximately 2% grade) What to do: Re-slope drain piping to ≥1/50 (2%) grade + upgrade drain heater to ≥200W for ultra-low temperature environments (≤-35°C)

Drain Pan Heater Not Working → Drain Line Ice Blockage

Likely causes

Drain pan heater open-circuit → defrost water refreezes before draining, ice accumulates under pan

Defrost timing error — cooling restarts before drain heater activates, defrost water refreezes immediately

Drain pipe insufficient slope (<1/50) — pooled water freezes even with heater running

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