Mitsubishi City Multi PURY-P400 Service Handbook page 42

3) Discharge temperature control
The discharge temperature of the compressor (Td) is monitored during the operation. If the upper limit is exceeded, the
frequency is reduced by 5 Hz.
• Control is performed every 30 seconds, starting at 30 seconds after the start of compressor.
• The operating temperature is 124°C (No. 1 compressor) and 115°C (No. 2 compressor).
4) 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 has been performed by means of discharge temperature or high
pressure.
2 Amount of frequency fluctuation
The amount of frequency fluctuation is controlled in response to the evaporation temperature (Te) and the
condensation temperature (Tc) so that it will reach the target values.
3 Frequency control back-up by the bypass valve
Frequency control is backed-up by turning on (opening) the bypass valve (SV4a) when only No. 1 compressor is
operated at its lowest frequency.
• Cooling
After the compressor has been operated for 15 minutes and only No. 1 compressor is operated in un-load (its
lowest frequency), the bypass valve is turned ON when the low pressure (63 LS) reaches 0.098 MPa or less
and turned OFF when it reaches 0.196 MPa or more.
• Heating
After the compressor has been operated for 3 minutes and only No. 1 compressor is operated in un-load (its
lowest frequency), the bypass valve is turned ON when the high pressure (Pd) exceeds 2.65 MPa and turned
OFF when it reaches 2.35 MPa or less.
(4) Bypass - capacity control
The solenoid valves are bypass valves (SV1, SV4a and SV6a) that allow bypassing of the high pressure and low
pressure sides and solenoid valves (SV22 and SV32) that control the capacity control valve inside the compressor.
They operate as follows:
1) Bypass valve (SV6a) [SV6a is on (open)]
• As shown in the table below, control is performed by the operation and stopping of the No. 1 compressor and No. 2
compressor.
No. 1 compressor No. 2 compressor
In Stop
In Operation
In Operation
ON
OFF
0.098 MPa
ON
OFF
2.35 MPa
SV6a
In Stop OFF
In Stop ON
In Operation OFF
0.196 MPa
2.65 MPa
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