Mitsubishi Electric PQRY-P200YEM-A Service Handbook page 52

2) Pressure limit
The upper limit of high pressure (Pd) is set for each frequency.
When the limit is exceeded, frequency is reduced every 10 seconds.
(Frequency decrease rate (Hz) : 22% of the present value)
<P200>
3) Discharge temperature limit
Discharge temperature (Td) of compressor is detected during operation. If the upper limit is exceeded, the fre-
quency is reduced. (Change rate : 5% of the present value)
• 30 seconds after starting compressor, control is performed every minute.
• Operation temperature is 130°C.
4) Periodical frequency control
Frequency controll is periodically performed except for the frequency controls at operation start, status change, and
protection.
1 Cycle of periodical frequency control
Periodical frequency control is performed every minute after the time specified below has passed.
• 20 sec after starting compressor
• 20 sec after frequency control by discharge temperature or pressure limit
2 Amount of frequency change
The amount of frequency change is controlled corresponding to evaporation temperature and high pressure
saturation temperature.
3 Back up of frequency control by bypass valve
During 20Hz operations, frequency is backed up by turning on (opening) bypass valve (SV2).
• Cooling
During 20Hz operations 3 minutes after starting compressor, bypass valve is turned on when,
Ps is 0.15MPa or less and turned off when Ps is 0.25MPa or more.
• Heating
During 20Hz operations 3 minutes after starting compressor, SV2 turned on when high pressure (Pd) exceeds
pressure limit and turned off when Pd falls to 20kg/cm
(5) Oil return control (Electronic expansion valve <SLEV>)
• Oil return LEV (SLEV) opening is dependent on compressor frequency and ambient temperature.
• SLEV is closed (0) when compressor stops, and SLEV is set (50) for 10 minutes after starting compressor.
(6) Sub cool coil control (LEV1) : PQHY
• The amount of super heat detected from the bypass outlet temperature of subcool coil (TH8) is controlled to be
within a certain range for each 30 seconds.
• The opening angle is corrected and controlled depending on the outlet/inlet temperature of subcool coil (TH5, TH7)
and the discharge temperature.
• However, the valve will be closed (0) at heating and compressor stopping.
• It will fully open during defrosting.
ON
OFF
0.15MPa 0.25MPa
<P250>
2 G (1.96MPa) or less.
ON
OFF
1.96MPa 2.65MPa
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