Defrost Control (Reverse Defrost Method) - Toshiba HFCR407C Service Manual

Item Operation explanation and applied data, etc.
12. Defrost (1) Conditions for starting the defrost operation
control 1) Calculate the operation time when the TE sensor detects below – 1°C during
(reverse heat mode. When the compressor is activated, start defrost after 25 minutes for
defrost the first time and after 55 minutes for the second time and thereafter.
method)
(2) How the controlling system works
1) For the master outdoor units
The control operates the inverters at the minimum frequency. When the inverter
ODU frequency is set minimum, a defrosting signal is sent to the slave outdoor
units. The 4-way valves and the outdoor fans go off one after another. The
maximum frequency of the inverter ODU is 90Hz.
2) For the slave outdoor units
• When the conditions for the defrost operation are all satisfied, a defrost
signal is sent to the master outdoor units.
• Once the signal is received, the 4-way valves go off and then the outdoor fan
goes off.
• While the defrost control is in progress, the compressors are all switched on.
(3) Conditions for finishing the defrost operation
1) Common condition
Once a certain period of time passed after the 4-way valves were off, the control
finishes the defrost operation according to the TE sensor detected temperature
and the Pd pressure. Defrost will be compulsorily ceased 10 minutes after it
was activated.
2) For the master outdoor units
Once the above common condition is satisfied and the slave outdoor units have
finished sending the defrost signal, the whole defrost operation is . . . complete.
3) Slave outdoor units
• When the condition for completing the defrost operation is satisfied, they
finish sending the defrost signal to the master outdoor units.
• When the condition for completing the defrost operation is satisfied and they
finish receiving the signal to stop defrost from the master outdoor units, the
defrost operation is complete.
(4) Control of completion of the defrost operation
1) For the master outdoor units
The control sets the outdoor fans with the maximum frequency 5 minutes after
the 4-way valves are switched on. The controller controls the heating fans
thereafter.
2) For the master outdoor units
• The inverter ODU is operated at the minimum frequency. If the compressors
are off, they will be activated and if they are already on, they will be held
constant. If a slave outdoor unit is connected, a signal to end the defrost
operation will be sent.
• The control then switches on the 4-way valves and completes sending the
defrost signal to the indoor units.
Outline of control
Outdoor units
61
Remarks
• If the conditions are
satisfied, all the
outdoor units should
start defrost mode
simultaneously.
• When the outdoor
units are combined,
the defrost operation
is compulsorily
completed for at
least 2 minutes.
• If the conditions are
satisfied, all the
outdoor units should
finish defrost mode
simultaneously.
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