Mitsubishi Heavy Industries SRK25GZ-L1 Handbook page 145

(g) Low Hz continuous operation protection control
The following controls are performed to return the oil to the compressor when the outdoor frequency is less than 34 Hz and
other than 0 Hz for 20 continuous minutes or more.
1) Forced operation at outdoor frequency of 34 Hz is performed for 2 minutes.
2) The outdoor fan operates according to decision frequency and the expansion valve operates according to the outdoor
frequency.
3) If the unit receives a command of that is higher than 34 Hz when operating at the forced 34 Hz, it will respond to the
higher command and the operation of this control is ended.
(h) High Hz continuous operation protection control
The following controls are performed to protect the compressor when the outdoor frequency is 92 Hz or higher for 9 continu-
ous minutes or more.
1) Forced operation at outdoor frequency of 90 Hz is performed for 1 minute.
2) The outdoor fan operates according to decision frequency and the expansion valve operates according to the outdoor
frequency.
3) After operating at 90 Hz for 1 minute, the outdoor frequency is raised to the decision frequency at a rate of 2 Hz every
4 seconds. This control is finished when outdoor frequency reaches the decision frequency or when the decision fre-
quency has become lower than the outdoor frequency.
4) If the unit receives a command of that is lower than 90 Hz when operating at the forced 90 Hz, it will respond to the
higher command and the operation of this control is ended.
(i) Heating low temperature protection control
The following controls are performed during heating operation when operating at an outdoor frequency other than 0 Hz and
the temperature detected by the outdoor air temperature thermistor is 2°C or less for 1 continuous minute.
1) The fan speed of the outdoor unit is forced one speed higher.
2) When the outdoor air temperature sensor reaches 4°C or more, the operation of this control is ended.
(j) Inching protection control
1) The following controls are performed to prevent the refrigerant oil from becoming diluted by refrigerant melting into it
when the compressor is being frequently started and stopped while under thermostat control. They are performed when
the outdoor air temperature sensor detects a temperature of 22°C or less during cooling or a temperature of 0°C or less
during heating for 1 continuous minute.
Decision frequency
Outdoor frequency
Hot Standby
Solenoid valve
(SVDf)
2) Restoration is made when the outdoor air temperature thermistor detects a temperature of 24°C or more during cooling
or a temperature of 2°C or more during heating.
(k) Current safe control
1) When the converter input current detected by the current sensor (CT) exceeds the set value, the frequency is reduced by
2 Hz. Checks are performed every second following this and if the current still exceeds the setting, the frequency is
reduced by another 2 Hz.
2) When the frequency is 16 Hz or less, this control will operate twice in one hour and then perform an abnormal stop. At
the same time, LED 2 on the printed circuit board for the outdoor unit will flash 3 times at 0.5 second intervals every 8
seconds. Note that on the first operation, the unit can be restarted after setting the compressor to stop mode.
(l) Current cut
An abnormal stop is made if the converter output current at the shunt resistor exceeds the set value. At the same time, LED
2 on the printed circuit board for the outdoor unit will flash 1 time at a 0.5 second interval every 8 seconds.
If current cut is operated again at less than 28 Hz when restarting from the stop mode, a third start cannot be performed. (The
timer lamp on the indoor unit will flash 1 time.)
0 Hz
ON
OFF
ON
OFF
Stop mode
1 minute
2 minutes
2 minutes 55 seconds
SCM-HG (4 room)
143