Defrost Flow Sequence
The defrost cycle operates based on the compressor’s cumulative run time, outdoor temperature, and outdoor heat exchanger temperature readings. The process automatically initiates, proceeds, and ends under the following conditions.
Heating Operation Start
Condition: Compressor begins operation.
Note: Defrosting is inhibited for the first 10 minutes after compressor startup.
Defrost Initiation Criteria
| Defrost Type | Compressor Operation Condition | Temperature Condition |
|---|---|---|
| 1st Defrost Cycle | Over 22 minutes | Outdoor heat exchanger temperature ≤ –9°C |
| Over 62 minutes | Outdoor heat exchanger temperature ≤ –5°C | |
| 2nd and Subsequent Defrosts | Over 35 minutes | (Tn – Tn10) ≤ –5°C and (Tn – Tnb) ≤ –2°C (However, Tn ≤ –6°C) |
| Integrating (Continuous) Defrost | Less than 10 minutes and 40 compressor OFF counts | — |
| Over 240 minutes (long operation) | Outdoor heat exchanger temperature ≤ –3°C | |
| Over 215 minutes (extended continuous operation) | Outdoor heat exchanger temperature ≤ –5°C |
Definitions:
Tn10 = Coil temperature during 10 minutes of continuous compressor operation.
Tnb = Average coil temperature over the previous 5 minutes.
Defrost Start
Once any of the above conditions are met, defrost begins.
Indicators:
Operation lamp flashes ON for 7 seconds / OFF for 2 seconds.
Control Actions During Defrost:
Compressor temporarily stops.
Outdoor fan motor stops.
After 30 seconds, the 4-way valve de-energizes (OFF).
After 35 seconds, the compressor restarts at 75 Hz.
Defrost Termination Conditions
Defrost operation ends automatically when one of the following occurs:
| Condition | Threshold |
|---|---|
| Outdoor heat exchanger temperature | Rises above +13°C |
| Compressor operation time | Reaches 15 minutes maximum |
End of Defrost Cycle
The system exits the defrost sequence and automatically resumes heating operation.
Indicator light returns to normal operation.
Summary
The system continuously monitors outdoor temperature and compressor runtime to determine when frost accumulation warrants a defrost cycle. Each defrost event is optimized for efficiency—short cycles clear minor frost, while longer, integrating cycles handle heavy frost conditions during extended operation.
