Mitsubishi Electric CITY MULTI PUHY-80TMU-A Service Handbook page 30

(4) Frequency control
• Depending on capacity required, capacity control change and frequency change are performed to keep constant
evaporation temperature (0˚C) in cooling operations, and high pressure (18kg/cm
• Frequency change is perfprmed at the rate of 3Hz/second across 20 ~ 110Hz range.
1) Frequency control starting
• 60Hz is the upper limit for 3 minutes after starting.
• 75Hz is the upper limit within 2 hours after turning on power source, and 30 minutes after starting compressor.
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)
3) Discharge temperature limit
Discharge temperature (Td) of compressor is detected during operation. If the upper limit is exceeded, the frequency
is reduced. (Change rate : 5% of the present value)
• 30 seconds after starting compressor, control is performed every minute.
• Operation temperature is 130˚C (266°F).
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 or finishing defrostoing operations
• 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 (ET) and high pressure
(Pd).
25 (356)
23 (327)
22 (313)
kg/cm
25 (356)
24 (341)
22 (313)
kg/cm
- 27 -
–30–
2
G) in heating operation.
<80TM>
2 G (psi)
<100TM>
2 G (psi)