GENERAL Assist Technical Reference
VII Protective Function List - Outdoor Unit
Outdoor unit protection controls, stop conditions and displayed fault codes
Use this reference when assessing an outdoor unit that is limiting operation, stopping a compressor or displaying a protection code.
Important: A protective function may operate without displaying an error code. Where the source table shows a dash (—), the outdoor unit is controlling operation to protect the system rather than reporting a permanent fault.
1. Protection codes at a glance
| Display | Protective function | Result |
|---|---|---|
| P1 | Discharge Temperature Protection Stop | Corresponding compressor stopped. |
| EA11 (INV) EA21 (CONST) | Repeated Discharge Temperature Protection Stop | Corresponding compressor permanently stopped; error displayed. |
| P2 | High Pressure Protection Stop | All compressors or the corresponding compressor stopped, depending on the protection. |
| EA41 | Repeated High Pressure Protection Stop 1 | All outdoor-unit compressors permanently stopped; error displayed. |
| EA42 (INV) EA43 (CONST) | Repeated High Pressure Protection Stop 2 / pressure switch operation | Corresponding compressor permanently stopped; error displayed. |
| P3 | Low Pressure Protection Stop | All outdoor-unit compressors stopped. |
| EA51 | Repeated Low Pressure Protection Stop | All outdoor-unit compressors permanently stopped; error displayed. |
| P4 | Compressor Temperature Protection Stop | Corresponding compressor stopped. |
| EA31 (INV) EA32 (CONST) | Repeated Compressor Temperature Protection Stop | Corresponding compressor permanently stopped; error displayed. |
| E941 | Overcurrent Break Stop - INV compressor | INV compressor stopped; repeated operation can become permanent. |
| E931 | INV compressor abnormal current at start-up | INV compressor stopped; repeated operation can become permanent. |
| E922 | Overcurrent Break Stop - constant-speed compressor | Constant-speed compressor permanently stopped; error displayed. |
| EAC4 | Repeated Heatsink Temperature Protection Stop | INV compressor permanently stopped; error displayed. |
Permanent-stop codes: Where the table identifies a permanent stop, do not simply reset the equipment repeatedly. Investigate the cause of the protection before returning the system to service.
2. Discharge temperature protection
| Function | Display | Starting / reset condition | Outdoor-unit action |
|---|---|---|---|
| Discharge Temp Protection 1 | — | Starts after 3 minutes of operation when discharge temperature reaches the protection threshold. Reset is based on discharge temperature and suction superheat returning below the specified limits. | EEV of the operating indoor unit is gradually opened. |
| Discharge Temp Protection 2 | — | Cooling: starts at discharge temperature ≥95°C; resets below 90°C. Heating: starts at ≥102°C; resets below 97°C. | EEV2 is opened by approximately 30 pulses every 30 seconds. |
| Discharge Temp Protection 3 | — | Starts at discharge temperature ≥107°C. Resets at discharge temperature ≤105°C. | Outdoor-unit rotation is executed. After the first rotation, it is executed every 15 minutes while the condition remains. |
| Discharge Temp Protection 4 | — | Starts at discharge temperature ≥105°C. Resets at ≤100°C. | INV compressor speed is reduced by 5 rps every 30 seconds and speed increase is prohibited. Speed-rise prohibition is cancelled when discharge temperature falls below 105°C. |
| Discharge Temp Protection 5 | — | Starts at discharge temperature ≥95°C with EEV1 ≤500 pulses. Reset after 2 minutes and when the source-table reset criteria are satisfied. | Expansion valve of a stopped indoor unit is gradually opened, up to approximately 200 pulses. |
| Discharge Temp Protection 6 | — | Starts at discharge temperature ≥90°C. Resets below 90°C. | EEV1 is forcibly opened. |
| Discharge Temp Protection Stop | P1 | Pattern 1: discharge temperature reaches the fixed stop value (INV 110°C; constant-speed 115°C). Reset after 3 minutes and discharge temperature ≤80°C. | Corresponding compressor is stopped. |
| Repeated Discharge Temp Protection Stop | EA11 (INV) EA21 (CONST) | Pattern 2 is generated twice within 40 minutes. Reset requires error reset after power is turned on again. | Corresponding compressor is permanently stopped and the error is displayed. |
3. High pressure protection
| Function | Display | Starting / reset condition | Outdoor-unit action |
|---|---|---|---|
| High Pressure Protection 1 | — | Starts at high pressure ≥3.94 MPa. Reset after the specified time and when high pressure is ≤3.70 MPa. | Solenoid-valve control is used to reduce pressure. |
| High Pressure Protection 2 | — | Starts at high pressure ≥3.50 MPa. Reset after 3 minutes and high pressure ≤2.80 MPa. | Solenoid-valve control is used according to compressor operating mode. |
| High Pressure Protection 3 | — | Starts at high pressure ≥3.50 MPa after the source-table fixed time. Reset is based on operation data and pressure falling below the specified limit. | Fan speed is increased one step. |
| High Pressure Protection 4 | — | Pressure-based fan protection with separate patterns around 3.3 to 3.5 MPa. | Fan speed is lowered every 30 seconds, or fixed to the lowest speed (approximately 300 rpm), depending on the pattern. |
| High Pressure Protection 5 | — | Starts at high pressure ≥3.20 MPa. Resets below 3.20 MPa. | Compressor capacity is lowered every 15 seconds. |
| Abnormal High Pressure Protection Control | — | Pattern 1 begins at high pressure ≥3.78 MPa; Pattern 2 begins at ≥3.90 MPa. Reset after 25 seconds when pressure returns below the applicable threshold. | Compressor capacity rise is prohibited or capacity is reduced every 10 seconds. |
| High Pressure Protection Stop 1 | P2 | Pattern 1 starts at high pressure ≥4.00 MPa. Reset after 5 minutes and high pressure ≤3.50 MPa. | All compressors in the outdoor unit are stopped. |
| Repeated High Pressure Protection Stop 1 | EA41 | Pattern 2 is generated 3 times within 60 minutes. Reset after 10 minutes and high pressure ≤3.50 MPa. | All compressors in the outdoor unit are permanently stopped; error displayed. |
| High Pressure Protection Stop 2 | P2 | Pressure switch operates at approximately 4.20 MPa. Reset after 5 minutes from pressure-switch reset; switch resets at approximately 3.2 MPa. | Corresponding compressor is stopped. |
| Repeated High Pressure Protection Stop 2 | EA42 (INV) EA43 (CONST) | Pattern 2 is generated 3 times within 60 minutes. Reset after 10 minutes from pressure-switch reset. | Corresponding compressor is permanently stopped; error displayed. |
4. Low pressure protection
| Function | Display | Starting / reset condition | Outdoor-unit action |
|---|---|---|---|
| Low Pressure Protection 1 | — | Starts at low pressure ≤0.20 MPa. Reset after 5 minutes and low pressure ≥0.30 MPa. | SV1 ON. |
| Low Pressure Protection 2 | — | Starts at low pressure ≤0.10 MPa. Reset after 3 minutes and low pressure ≥0.17 MPa. | SV1 ON. |
| Low Pressure Protection 3 | — | Starts when one outdoor unit and the INV compressor operate at 30 rps and low pressure is ≤0.55 MPa. Reset after 5 minutes and when INV compressor speed is 40 rps or higher. | SV1 ON. |
| Low Pressure Protection 4 | — | Starts after 3 minutes with low pressure ≤0.18 MPa. Reset after 3 minutes and low pressure ≥0.22 MPa. | EEV of a stopped indoor unit is opened quickly to approximately 450 pulses. |
| Abnormal Low Pressure Protection Control | — | Starts at low pressure ≤0.16 MPa. Reset after 3 minutes and low pressure ≥0.18 MPa. | Compressor capacity is lowered every 180 seconds; if low pressure recovers above the specified level, compressor capacity rises. |
| Low Pressure Protection Stop | P3 | Pattern 1: low pressure ≤0.05 MPa, or low pressure ≤0.10 MPa continues for 10 minutes. Reset after 3 minutes and low pressure ≥0.17 MPa. | All compressors in the outdoor unit are stopped. |
| Repeated Low Pressure Protection Stop | EA51 | Pattern 2 is generated 5 times within 180 minutes. Reset requires error reset after power is turned on again. | All compressors in the outdoor unit are permanently stopped; error displayed. |
5. Compressor, overcurrent and inverter protection
| Function | Display | Starting / reset condition | Outdoor-unit action |
|---|---|---|---|
| Compressor Temp Protection Stop | P4 | Pattern 1 starts when compressor temperature reaches the fixed value (INV 112°C; constant-speed 120°C). Reset after 3 minutes and discharge temperature ≤80°C. | Corresponding compressor stopped. |
| Repeated Compressor Temp Protection Stop | EA31 (INV) EA32 (CONST) | Pattern 2 is generated twice within 40 minutes. Reset requires error reset after power is turned on again. | Corresponding compressor permanently stopped; error displayed. |
| Overcurrent Break Stop - INV compressor | E941 | INV compressor is stopped when the overcurrent protection circuit in the inverter PCB detects abnormal current during operation. If repeated 5 times, the INV compressor becomes a permanent stop. | INV compressor stopped. |
| INV compressor abnormal current at start-up | E931 | Inverter PCB detects abnormal current at compressor start-up. If repeated over the specified number of attempts, a permanent stop occurs. | INV compressor stopped. |
| Overcurrent Break Stop - constant-speed compressor | — | Starts when constant-speed compressor current is ≥19.5 A continuously for 2 seconds. Pattern 1 resets 10 minutes after the compressor is stopped. | Constant-speed compressor stopped. |
| Repeated constant-speed overcurrent stop | E922 | Pattern 2 is generated twice within 60 minutes. Reset requires error reset after power is turned on again. | Constant-speed compressor permanently stopped; error displayed. |
| Heatsink Temp Protection Stop | — | Starts at heatsink temperature ≥80°C. Reset after 10 minutes and heatsink temperature ≤75°C. | INV compressor stopped. |
| Repeated Heatsink Temp Protection Stop | EAC4 | Pattern 2 is generated 3 times within 60 minutes. Reset after 10 minutes and heatsink temperature ≤75°C. | INV compressor permanently stopped; error displayed. |
| Frequency Maximum Setting Protection - INV compressor | — | Protection responds to inverter compressor current. One stage starts around 18.2 A and another around 19.2 A, with reset below the same respective current thresholds. The start current value is changed by outside temperature. | INV compressor speed increase is prohibited or compressor speed is lowered. |
6. Diagnostic approach
| 1 | Identify the displayed code, if any, and confirm which protective function has operated. |
| 2 | Check the relevant detected part: discharge-temperature thermistor, high-pressure sensor/switch, low-pressure sensor, compressor-temperature thermistor, current detector circuit or heatsink thermistor. |
| 3 | Confirm whether the protection is a temporary control action, a compressor stop or a permanent stop. |
| 4 | Investigate the refrigeration, airflow, valve, sensor and electrical conditions that could have caused the measured value to exceed the protection threshold. |
| 5 | Only reset a permanent-stop error after the cause has been identified and rectified. |
Source: Service manual section 2-6-1, Protective Function List - Outdoor Unit. Values and terminology above are transcribed from the supplied reference pages. Always confirm the applicable service manual for the exact outdoor-unit model before diagnosis or component replacement.