Defrost Operation Control - Fujitsu ASU18RLF Service Instructions Manual

26. DEFROST OPERATION CONTROL

1. CONDITION OF STARTING THE DEFROST OPERATION
The defrost operation starts when the outdoor heat exchanger temperature sensor detects
the temperature lower than the values shown in Table 20, 21, 22 .
1-1 NORMAL DEFROST
( Table 20 : Condition of starting defrost operation )
Normal defrost
Tn : Outdoor heat exchanger temp.
Ta : Outside air temp.
Tn-1 : Before 5 minutes detected Tn
1-2. INTEGRATING DEFROST
( Table 21 : Condition of integrating defrost operation )
Integrating defrost
( OFF count defrost )
1-3. INTEGRATING ( OFF COUNT ) DEFROST
( Table 22 : Condition of integrating ( OFF count ) defrost operation )
Integrating defrost
If the compressor continuous operation time is less than 10 minutes,
the OFF number of the compressor is counted.
If any defrost operated, the compressor OFF count is cleared.
2. CONDITION OF THE DEFROST OPERATION COMPLETION
Defrost operation is released when the conditions become as shown in Table 23 .
( Table 23 : Defrost release condition )
Outdoor heat exchanger temperature sensor value is higher than 59°F(15°C) or
Compressor operation time has passed 15 minutes.
Compressor integrating operation time
Less than 35 minutes
Tn < 1.4°F(-17°C)
=
(at Ta > 14°F(-10°C)
=
Tn < 0.8 × Ta - 11.6 or Tn < -18.4°F(-28°C)
=
(at 4°F(-20°C) < Ta < 14°F(-10°C))
Does not operate
Tn < 0.8 × Ta - 11.6
=
(at Ta < 4°F(-20°C))
Tn - Tn-1 < 28.4°F(-2°C) and Sn = Sn-1
(Tn < 21.2°F(-6°C))
=
: Number of operation indoor units
Sn
: Before 5 minutes detected Sn
Sn-1
Compressor integrating operation time
More than 210 minutes
( For continuous operation )
Tn < 26.6°F(-3°C)
=
(and after 30 minutes,
if the Tn < 26.6°F(-3°C)
=
Compressor integrating operation time
Less than 10 minutes
( For intermittent operation )
OFF count of the compressor 40 times
( at outside air temp. < 35.6°F(2°C))
Release Condition
01-26
More than 35minutes
=
=
or Tn < -18.4°F(-28°C)
=
Tn < 23°F(-5°C)
=
(and after 3 minutes,
if the Tn < 23°F(-5°C)
=