Lennox MPB018S4M - Defrost Control; Defrost Theory

163
NOTE: Average value of T2: Sum T2 value of all indoor units)/ (indoor units number). According to the nal capacity
request to conrm 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) 0
HEAT_
F1
HEAT_
F2
...
...
HEAT_
15
HEAT_
16
Amendatory capacity
demand
0 1 2
...
...
15 16
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