Conditions for Starting Defrost Operation
The defrost operation begins when the outdoor heat exchanger temperature sensor (Tn) detects a temperature lower than the thresholds specified in Table 19 below.
Table 19 – Conditions for Starting Defrost Operation
| Operation Stage | Compressor Integrating Operation Time | Condition to Start Defrost |
|---|---|---|
| First Defrost After Start-Up | Less than 22 minutes | Does not operate |
| 22 to 62 minutes | Tn ≤ –9°C | |
| More than 62 minutes | Tn ≤ –5°C | |
| Defrosting After Second or Subsequent Operations | Less than 35 minutes | Does not operate |
| More than 35 minutes | (Tn – Tn10) ≤ –5°C and (Tn – Tnb) ≤ –2°C However, Tn ≤ –6°C | |
| Integrating Defrost (Constant Monitoring) | More than 240 minutes (long continuous operation) | Tn ≤ –3°C |
| More than 215 minutes (extended continuous operation) | Tn ≤ –5°C | |
| Less than 10 minutes (intermittent operation)* | Defrost begins after 40 compressor OFF counts |
Notes:
Tn10: Temperature of continuous operation after 10 minutes.
Tnb: Average temperature over the past 5 minutes.
1: If the compressor’s continuous operation time is less than 10 minutes, the OFF count of the compressor is used to determine defrost initiation. Once defrost occurs, the OFF count resets.
2. Conditions for Completing Defrost Operation
The defrost cycle ends when one of the following conditions is met, as shown in Table 20 below.
Table 20 – Defrost Release Conditions
| Release Condition |
|---|
| Outdoor heat exchanger temperature sensor (Tn) rises above +13°C, or |
| Compressor operation time exceeds 15 minutes |
Summary
The defrost control logic monitors outdoor coil temperature and compressor operation time to prevent frost accumulation on the heat exchanger. Once the defrost conditions are met, the system automatically switches modes to melt accumulated frost and resumes heating once the temperature rises sufficiently or the cycle time limit is reached.