Toshiba MMY-MUP0721HT9P-UL Service Manual page 53

Item Description of operation, numerical data, and other information
5. Oil This is a control for preventing oil shortage in the compressor between the outdoor units,
recovery and oil equalization control is performed as follows during cooling operation and heating
control operation.
[1] During cooling operation
When the oil level of any compressor in the outdoor unit is determined to be insufficient
due to the stagnation of refrigerating machine oil in the gas pipes and the indoor unit
during cooling operation, this control recovers the oil from the indoor unit and evens oil
levels between the outdoor units by increasing the compression frequency of the outdoor
unit that detected drop of the oil level.
This control is managed by the header outdoor unit.
1) Control start condition
• The operating time of the compressor in which an insufficient oil level is detected
exceeds 15 minutes
• The operating time of the compressor in which an insufficient oil level is detected
exceeds 30 minutes
• The operating time of the compressor in which an insufficient oil level is detected
exceeds 45 minutes
• When the operating time of the compressor in which an insufficient oil level is
detected exceeds 60 minutes, it causes an abnormal stop of the compressor.
2) Control content
• The operating compressor is operated at the target speed, the stopped compressor
is started, and the compressor is operated at the target speed.
• Switch control mode in the indoor unit to the cooling oil (refrigerant) recovery control
mode, and open the PMV opening of the indoor unit by a certain opening.
• After the recovery control is performed for a predetermined time, the recovery control
ends and the normal cooling operation is resumed.
[2] During heating operation
This control can recover the stagnated oil in the piping or indoor heat exchanger and
return it to the compressor by defrosting operation when the oil level continues to
decrease even if the compressor oil level has been detected and the oil return control
from the oil separator has functioned.
Reverse defrost control is performed every 15 minutes after an insufficient oil level is
•
confirmed during heating operation.
• When the operating time of the compressor in which an insufficient oil level is
detected exceeds 60 minutes, it causes an abnormal stop of the compressor.
6. Heating Since the indoor unit that is stopped during heating operation closes the PMV, liquid
refrigerant refrigerant may accumulate in the heat exchanger, resulting in a refrigerant shortage
(oil) recovery condition. This control is to recover the liquid refrigerant to return it to the outdoor unit
control when a refrigerant shortage is detected.
The PMV opening of the stopped indoor unit is slightly opened to return the refrigerant to
the outdoor unit, but if the insufficient refrigerant state is still not resolved, heating
refrigerant recovery control is performed.
This control also recovers the refrigerant in Indoor/Outdoor unit after defrosting and the oil
in the outdoor heat exchanger during heating overload operation. It is managed by the
header outdoor unit.
[1] Paused heating indoor unit PMV minute opening control
• Control start condition
When all the following conditions are satisfied
• There are units with heating thermostat ON and other than thermostat ON
(stop/thermostat OFF).
• When the outdoor unit determines the refrigerant shortage condition
• When the outdoor PMV opening exceeds the specified opening or the TD sensor
temperature exceeds the specified value
• Control content
When the control starts, the PMV in the indoor unit during stop opens by a minute opening.
[2] Heating refrigerant recovery control
Control start condition
• At the start of heating operation (when Comp. is turned on from Comp. OFF)
• During heating operation transition after defrosting
• 40 minutes have passed since the refrigerant shortage state was judged after starting
the PMV minute opening control in the paused heating indoor unit.
- 53 -
Remarks
• The shortage is confirmed
when the shortage
continues even if the
recovery operation (SV3D
valve is turned on) is
performed for each outdoor
unit when the shortage is
detected.
* Depending on the number
of indoor units when an
insufficient oil level is
confirmed, this control
determines whether to
recover the oil from only the
operating indoor units or all
the indoor units.
• Oil level confirmation timer
operates when an
insufficient oil level is
detected.
• The recovery duration
varies depending on
the load condition, but
it usually takes around
5-10 minutes.
• The compressor's
speed varies depending
on the control
conditions, indoor
capacity, and outdoor
unit.