Line Mini-Split Heat Pump Series
41 codes
/
Protection

P4 Refrigeration Overload Protection

LED

What it means

The outdoor coil sensor is detecting excessive temperature. The system is actively reducing compressor frequency to prevent overloading.

Inspection path

1 Outdoor coil sensor resistance → 2 System pressure (check for dirty blockage) → 3 Outdoor fan speed → 4 Voltage dividing resistance in outdoor controller coil sensor circuit

Diagnostic procedure

  1. Check the outdoor coil sensor with a multimeter. Standard resistance is 20KΩ at 25°C.
  2. Use a pressure gauge to check system pressure. High pressure may indicate dirty internal blockage or poor external heat transfer, both of which drive up coil temperature.
  3. Observe the outdoor fan speed. A slow-running fan reduces heat transfer and raises coil temperature.
  4. Use a multimeter to check the voltage-dividing resistance in the outdoor controller's coil sensor circuit. If uncertain, replace the outdoor controller and observe whether the protection clears.

Tools

  • Multimeter
  • Pressure gauge

Frequent parts

  • Coil sensor
  • Condenser (dirty)
  • Outdoor fan
  • Outdoor unit controller

Sensors referenced

Safety Disconnect power at the breaker before opening any access panel. DC bus capacitors retain charge for up to 5 minutes after disconnect - verify with a meter before touching live components.
Sensor Reference 6

Internal temperature

15 kΩ @ 25°C
Too-high resistance Detected temperature reads lower than actual. May cause shutdown errors in heating mode or startup failures in cooling mode.
Too-low resistance Detected temperature reads higher than actual. May cause startup errors in heating mode or shutdown failures in cooling mode.
Triggers E1 Internal Temperature Sensor Error

External coil

20 kΩ @ 25°C
Too-high resistance Detected temperature reads lower than actual. May cause frequent entry into defrost mode, illusory defrost cycles, or protection errors during cooling.
Too-low resistance Detected temperature reads higher than actual. May cause defrost failures during heating or protection activation during cooling.
Triggers P4 Refrigeration Overload Protection E2 External Coil Sensor Error

Internal coil

20 kΩ @ 25°C
Too-high resistance Detected temperature reads lower than actual. May cause high-pressure cold-blast protection during heating or frequent anti-freezing protection during cooling.
Too-low resistance Detected temperature reads higher than actual. May cause frequent overheat protection during heating or overload protection during cooling.
Triggers P6 Indoor High Temperature Protection P7 Anti-Freezing Protection in Refrigeration Mode E3 Internal Coil Sensor Error

Exhaust

50 kΩ @ 25°C
Too-high resistance Detected exhaust temperature reads lower than actual. The system may fail to activate protection when exhaust temperature is genuinely dangerous.
Too-low resistance Detected exhaust temperature reads higher than actual. The unit enters high exhaust temperature protection frequently, compressor frequency threshold rises, leading to unwanted shutdowns. Example: installing a 20KΩ coil sensor in place of the 50KΩ exhaust sensor produces this behavior.
Triggers F4 Exhaust Sensor Error P5 Exhaust Protection

External temperature

15 kΩ @ 25°C
Too-high resistance Detected outdoor temperature reads lower than actual, causing incorrect temperature-based control decisions.
Too-low resistance Detected outdoor temperature reads higher than actual, causing incorrect temperature-based control decisions.
Triggers F6 External Temperature Sensor Error

Recirculated

20 kΩ @ 25°C
Too-high resistance Incorrect back temperature value affects electronic expansion valve adjustment and four-way valve position confirmation during heating.
Too-low resistance Incorrect back temperature value affects electronic expansion valve adjustment and four-way valve position confirmation during heating.
Triggers FA Recirculated Sensor Error