R-Pro › Field cases › Refrigeration systems

Electric Heater Defrost Overtime → Evaporator Thermal Shock and Case Deformation

Likely causes

Defrost termination sensor (thermistor) open-circuit or misconnected → heater runs to max timer without temperature sensing

Check: Measure sensor terminal resistance: ~10kΩ at 0°C, ~6.8kΩ at +10°C. ∞ or 0Ω indicates open/short

What to do: Replace thermistor with same-spec NTC 10kΩ@25°C if open/short → recheck wiring → verify operation

Defrost termination setpoint too high (above +20°C) → heater overheats

Check: Check defrost termination setpoint in controller menu (normal +8 to +12°C)

What to do: Set termination temperature to +8–+12°C → confirm backup timer is ≤25 min

No maximum time limit set on backup timer → heater runs excessively long

Check: Check timer settings — verify maximum defrost time is set to ≤25 min

What to do: Set maximum defrost time to 25 min → ensures forced cutoff after 25 min even if temperature sensor fails

Field tip

Setting the backup timer to 25 min is the minimum field safety net — even if the termination sensor fails, defrost is forced off after 25 min.

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