General Assist Technical Reference
Defrost Logic
Defrost operation control, release conditions and OFF defrost logic
This reference explains how the system determines when to start and stop defrost during heating operation. Defrost is controlled using compressor accumulated operating time together with outdoor heat exchanger temperature.
Important: The values below are model-specific control thresholds taken from the applicable service information. Always confirm the correct service manual when diagnosing a specific unit.
1. First defrost operation
From heating start, the first defrost is determined by compressor accumulated operating time and outdoor heat exchanger temperature.
| Compressor accumulated operating time | Defrost start condition |
|---|---|
| Less than 17 minutes | Defrost does not operate. |
| More than 17 minutes | Outdoor heat exchanger temperature is below -9°C. |
| More than 57 minutes | Outdoor heat exchanger temperature is below -5°C. |
2. Second and subsequent defrost operations
| Compressor accumulated operating time | Defrost start condition |
|---|---|
| Less than 35 minutes | Defrost does not operate. |
| More than 35 minutes | Outdoor heat exchanger temperature is below -10°C. |
3. Integrating defrost - constant monitoring
| Condition | Defrost start requirement |
|---|---|
| Long continuous operation | Compressor accumulated operating time is more than 210 minutes and outdoor heat exchanger temperature is below -3°C. |
| Intermittent operation | When compressor continuous operating time is less than 10 minutes, the compressor OFF count is monitored. Defrost starts when the OFF count reaches 40 times. |
Note: If any defrost operation occurs, the compressor OFF count is cleared.
4. Defrost completion / release condition
Once defrost has started, it ends when either of the following release conditions is met:
| Release condition |
|---|
| Outdoor heat exchanger temperature rises above 10°C. |
| Compressor operating time during defrost reaches a maximum of 15 minutes. |
5. Defrost operating sequence
| Step | Operation |
|---|---|
| 1 | Heating operation starts with compressor ON. Defrost is inhibited for the first 10 minutes. |
| 2 | When one of the applicable first, subsequent or integrating defrost conditions is satisfied, defrost starts. |
| 3 | Defrost indicator / operation lamp flashes approximately 7 seconds ON / 2 seconds OFF. |
| 4 | Compressor turns OFF and outdoor fan motor turns OFF. |
| 5 | Approximately 30 seconds later, the 4-way valve turns OFF. |
| 6 | Approximately 36 seconds later, the compressor turns ON. |
| 7 | Defrost ends when the outdoor heat exchanger is above 10°C or compressor ON time reaches 15 minutes. |
6. OFF defrost operation control
When heating operation is stopped while frost is present on the outdoor heat exchanger, the system may automatically perform an OFF defrost before finally stopping.
OFF defrost start condition: During heating operation, the outdoor heat exchanger temperature is below -4°C and the compressor accumulated operating time is more than 30 minutes.
OFF defrost sequence
| Step | Operation |
|---|---|
| 1 | Heating operation stops. |
| 2 | If the outdoor heat exchanger is below -4°C and compressor accumulated operation exceeds 30 minutes, OFF defrost starts. |
| 3 | The operation lamp flashes approximately 7 seconds ON / 2 seconds OFF. |
| 4 | Defrost continues until the outdoor heat exchanger temperature rises above 10°C or compressor ON time reaches 15 minutes. |
| 5 | Defrost ends and the unit stops. |
7. Quick reference
| Control stage | Time requirement | Outdoor heat exchanger temperature |
|---|---|---|
| 1st defrost - early | More than 17 min | Below -9°C |
| 1st defrost - later | More than 57 min | Below -5°C |
| 2nd and later | More than 35 min | Below -10°C |
| Integrating defrost | More than 210 min | Below -3°C |
| OFF defrost | More than 30 min | Below -4°C |
| Defrost release | Maximum 15 min | Above 10°C |