General Assist Technical Reference
Defrost Flow Chart - LATLs
Heating-mode defrost initiation and termination logic
During heating operation, defrost is controlled using a combination of compressor operating time, outdoor temperature and outdoor heat exchanger temperature. Defrost is inhibited for the first 10 minutes after heating operation starts.
1. Defrost entry conditions
| Defrost logic | Condition | Outdoor heat exchanger requirement |
|---|---|---|
| 1st defrost | Compressor integrating operation over 22 minutes | Below -9°C |
| 1st defrost - alternate condition | Compressor integrating operation over 62 minutes | Below -5°C |
| 2nd and later defrost | Compressor integrating operation over 35 minutes | Defrost condition is determined from outdoor and heat-exchanger temperature relationship: Tn - Tn10 < -5°C Tn - Tnb < -2°C however, Tn ≤ -8°C |
| Integrating defrost - compressor OFF count | Compressor OFF count reaches 40 times with each stop less than 10 minutes | Constant monitoring |
| Integrating defrost - long operation | Compressor integrating operation over 240 minutes | Below -3°C |
Important: The flow chart indicates that defrost will not start during the first 10 minutes after the compressor starts in heating mode.
2. What happens when defrost starts
- The defrost indicator / operation lamp flashes 6 seconds ON / 2 seconds OFF.
- The compressor turns OFF.
- The outdoor fan motor turns OFF.
- Approximately 30 seconds later, the four-way valve turns OFF.
- Approximately 35 seconds later, the compressor turns ON and the defrost cycle proceeds.
3. Defrost termination
Defrost ends when eitherof the following conditions is reached:
- Outdoor heat exchanger temperature rises to above +13°C; or
- Compressor ON time during defrost reaches the maximum of 15 minutes.
4. Technician quick reference
| Check | Expected behaviour |
|---|---|
| Immediately after heating starts | No defrost for 10 minutes. |
| Defrost demand | Determined by accumulated compressor run time together with outdoor and outdoor heat exchanger temperatures. |
| During defrost | Outdoor fan is OFF, valve position changes and compressor operation is controlled as shown above. |
| Maximum defrost duration | 15 minutes compressor ON time. |
| Normal end condition | Outdoor heat exchanger temperature above +13°C. |
Diagnostic note: If the unit is not entering defrost when expected, confirm the outdoor temperature sensor, outdoor heat exchanger thermistor readings and compressor operating history before assuming a control fault.
