Toshiba MMU-P0121H Service Manual page 33

Item
7. Defrost control (1) Start condition of defrost operation ...............................................
(Reverse
When 25 minutes has passed at the first time and 55 minutes at
defrost method)
the second time and later after the compressor was activated, by
counting the operation time when TE sensor detection
temperature became lower than –1°C in heating operation.
(2) Contents of control ........................................................................
1) Master outdoor unit
2) Terminal outdoor unit
(3) Stop conditions of defrost operation ..............................................
1) Common conditions
2) Master outdoor unit
3) Terminal outdoor unit
(4) Stop control of defrost operation
1) Master outdoor unit
2) Master outdoor unit
3) Terminal outdoor unit
Operation explanation and applied data, etc.
Drive the inverter with the minimum frequency. When
frequency of the inverter command is set to the minimum
frequency, the defrost signal is sent to the indoor unit and the
terminal outdoor unit. After then, turn off 4-way valve to stop
the outdoor fan. The upper limit of the inverter frequency is
90Hz during defrost control.
• When the defrost conditions are satisfied, the defrost signal
is sent to the master outdoor unit.
• After receiving the defrost signal from the master outdoor
unit, turn off 4-way valve. After then, stop the outdoor fan.
• During defrost control, turn on all the fixed-speed
compressors.
When the specified time has passed after 4-way valve was
turned off, the defrost operation completes based upon
conditions of TE sensor temperature detection value or Pd
pressure value. When 10 minutes have passed after start of
the defrost operation, finish the defrost operation manually.
The operation shifts to the defrost stop control when the
common conditions of the defrost stop operation have been
satisfied and the defrost signal has completed from all the
terminal outdoor units.
• When the common conditions of the defrost stop operation
have been satisfied, the defrost signal to the master outdoor
unit completes.
• The operation shifts to the defrost stop control when the
defrost stop conditions have been satisfied and the defrost
stop signal has been received from the master outdoor unit.
Set the outdoor fan to the maximum No. of waves 5 seconds
after turning on 4-way valve. The heating fan control is
performed after then.
• Drive the inverter with the minimum frequency. If the fixed-
speed compressor is off, turn on it, and keep ON status if
the fixed-speed compressor is on. When the terminal
outdoor unit is connected, send the defrost stop signal.
• After then, turn on 4-way valve to stop the defrost signal
which is being sent to the indoor unit.
• Keep ON status of the fixed-speed compressor 1 and 2.
If they are off, turn on the compressor.
• Turn on 4-way valve after the specified time has passed
from when the defrost stop signal was received from the
master outdoor unit.
• After then, execute control for compressor capacity based
upon compressor start/stop ON/OFF signal from the master
outdoor unit.
3-30
Remarks
• When the conditions are
satisfied, each outdoor
unit starts defrost
operation concurrently.
• When the outdoor units
are combined, the defrost
operation continues
forcibly for 2 minutes if
the defrost operation has
started once.
• When the outdoor units
are combined, the fan
driving may be controlled
by Pd pressure during
defrost operation.