Mitsubishi Electric CITY MULTI PUHY-P400YEM-A Service Handbook page 94

2 Switching No. 3 compressor from operation to stopping
When the required performance is exceeded with the No. 1 and No. 2 variable capacity unit compressors and the
constant capacity unit No. 3 compressor in operation, the No. 3 compressor will be stopped.
3) Pressure control
• The upper limit value for the high pressure (Pd) has been set for each frequency. When this value is exceeded, the
frequency is reduced every 30 seconds.
• While the constant capacity unit is in operation, if the high pressure (63HS) value exceeds 2.45 MPa, the constant
capacity unit compressor will be stopped.
4) Discharge temperature control
1 The discharge temperature of the compressor (Variable capacity unit: TH11, TH12, Constant capacity unit:
TH11) is monitored during the operation. If the upper limit is exceeded, the frequency is reduced by 5 Hz.
• Control is performed every 30 seconds after 30 seconds at the compressor starting.
• The operating temperature is 124˚C.
2 While the constant capacity unit is in operation, if the constant capacity unit discharge temperature (TH11)
exceeds 130˚C, the constant capacity unit compressor will be stopped.
5) Compressor frequency control
1 Ordinary control
The ordinary control is performed after the following times have passed.
• 30 seconds after the start of the compressor or 30 seconds after the completion of defrosting.
• 30 seconds after frequency control operation by the discharge temperature or the high pressure.
2 Amount of frequency fluctuation
The amount of frequency fluctuation is controlled in response to the evaporation temperature (TH2) and the high
pressure (Pd) so that it will be approached the target values.
3 Frequency control back-up by the bypass valve
Frequency control is backed-up by turning on (opening) the bypass valve (SV4) when only the No. 1 compressor
is operated at its lowest frequency.
• Cooling
After the compressor has been operated for 15 minutes and only the No. 1 compressor is operated in un-load
(its lowest frequency), the bypass valve is turned ON when the evaporation temperature (TH2) is – 30˚C or
less and turned OFF when it is – 15˚C or more.
• Heating
After the compressor has been operated for 3 minutes and only the No. 1 compressor is operated in un-load
(its lowest frequency), the bypass valve is turned ON when the high pressure (Pd) exceeds 2.45Mpa and
turned OFF when it is 1.96 MPa or less.
ON
OFF
– 30˚C – 15˚C
ON
OFF
1.96 MPa 2.45 MPa
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