Fujitsu AOUH18LPAS1, Service Manual

Page: 117 / 169

6. Defrost operation control
Tn: Outdoor unit heat exchanger temperature
Ta: Outdoor temperature
Tn10: Temperature at 10 minutes after compressor start
Tnb: Temperature before 5 minutes
•
Triggering condition
The defrost operation starts when outdoor unit heat exchanger temperature sensor detects the
temperature lower than the values shown below.
– 1st time defrosting after starting operation
Compressor integrating
operation time
Less than 17 min. 17 to 57 min. More than 57 min.
Condition Does not operate
Tn ≤ 15.8°F (-9°C) and
Tn-Ta ≥ 9.0°F (5°C)
Tn ≤ 23.0°F (-5°C)
– 2nd time and after
Compressor integrating
operation time
Less than 40 min. More than 40 min.
Condition Does not operate
Tn-Tn10 < -9.0°F (-5°C) (Tn ≤ 21.2°F [-6°C])
Tn-Tnb < -3.6°F (-2°C) (Tn ≤ 21.2°F [-6°C])
Tn ≤ 1.4°F (-17°C) (Ta ≥ 14.0°F [-10°C])
Tn ≤ 19.4°F (-7°C) or Tn ≤ -4.0°F (-20°C) (Ta <
14.0°F [-10°C])
– Integrating defrost (Constant monitoring)
Compressor integrating
operation time
More than 240 min. (For
long continuous
operation)
More than 213 min. (For
long continuous
operation
Less than 10 min.* (For
intermittent operation)
Condition Tn ≤ 26.6°F (-3°C) Tn ≤ 23.0°F (-5°C)
Count of the compressor
off: 40 times
*: If the compressor continuous operation time is less than 10 minutes, the number of the com-
pressor off is counted. If any defrost operated, the compressor off count is cleared.
•
Release condition
The defrost operation is released when either one of the conditions below is satisfied.
Outdoor unit heat exchanger temperature
(after 1 minute or later since compressor start)
60.8°F (16°C) or more
Compressor operation time 15 minutes
- (04-21) -
6. Defrost operation control
CONTROL AND FUNCTIONS CONTROL AND FUNCTIONS