Defrost Control; Defrost Theory - Lennox MPA009S4S Service Manual

NOTE:
Average value of T2: Sum T2 value of all indoor units)/ (indoor units number). According to the final capacity
request to confirm the operating frequency, as following table. Heating capacity improved in low ambient heating.
In heating mode, when T2<T2_ExitT4LowFre_ADD , and T4<-4°C, there is frequency elevation: elevated frequency=
Recent frequency * 110%
When T2> T2_ExitT4LowFre_ADD-2 and T4>-6, the highest frequency can't exceed F17
When T2> T2_ExitT4LowFre_ADD-4 and T4>-8, the highest frequency can't exceed F18
When T2> T2_ExitT4LowFre_ADD-6 and T4>-10, the highest frequency can't exceed F19
In the other conditions, the highest frequency is F20.
Frequency (Hz)
Amendatory capacity
demand

31.2. 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)

31.3. Defrost Theory

Defrost will be initiated if any one of the following is reached, in the following sequence:
1. After 29 minutes of run-time T3 is less than 19.4°F AND T3+4.5°F is less than or equal to T30, then defrost will
initialize.
2. After 35 minutes of run-time, T3 is lower than 23°F AND T3+5.4°F is less than 30°F.
3. After 40 minutes of run-time of T3 being lower than 11.2°F.
4. After 2 hours of run-time if T3 is lower than 5°F.
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
HEAT_
0
F1
0 1
...
HEAT_
F2
...
...
2
...
163
HEAT_ HEAT_
15 16
15 16