Lennox Mini-Split Service Manual / Page 256
Defrost Control
For defrost calculations:
T3 = Outdoor coil temperature sensor
T30 = Minimum value of T3 during 10 to 15 minutes
of runtime time period.
Defrost mode begins when any one of the following
conditions are met:
1. After 29 minutes of runtime
T3 < 19.4°F (-7°C) and T3 + 4.5°F (2.5°C) ≤ T30
2. After 35 minutes of runtime
T3 < 23°F (-5°C) and T3 + 5.4°F (3°C) ≤ T30
3. After 40 minutes of runtime
T3 < -11.2°F (-24°C) for 3 minutes
4. After 120 minutes of runtime
T3 < 5°F (-15°C)
Defrost mode ends when any of the following
conditions are met.
1. T3 > 64.4°F (18°C)
2. T3 remains > 43.4 °F (8°C) for 80 seconds
3. System has been in defrost mode for 10 minutes
Compressor
4-Way valve
Outdoor fan
10S
10S
X2
X1
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