Mitsubishi Electric CITY MULTI PUHY-400YMF-B Service Handbook page 72

• The operating temperature is 124°C.
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 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 the turning on (opening) the bypass valve (SV4) when only the No. 1 com-
pressor 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 25 kg/cm
MPa) and turned OFF when it is 20 kg/cm
(4) Bypass - capacity control
The solenoid valves have bypass valves (SV1, SV4 and SV6) 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 (SV6) [SV6 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
Stop
Operate
Operate
ON
OFF
– 30°C
2 (1.96 MPa) or less.
ON
OFF
2
20 kg/cm G 25 kg/cm
(1.96 MPa) (2.45 MPa)
SV6
Stop OFF
Stop ON
Operate OFF
– 15°C
2
G
–69–
2 (2.45