Toshiba MM-A0160HX, Service Manual

Page: 39 / 135

40
11
Outline of Control
Outdoor Units
Item Operation explanation and applied data, etc. Remarks
12. Defrost
control
(reverse
defrost
method)
(1) Conditions for starting the defrost operation
1) Calculate the operation time when the TE sensor
detects below – 1°C during heat mode. When the
compressor is activated, start defrost after
25 minutes for the first time and after
55 minutes for the second time and thereafter.
(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.
• 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.