Mitsubishi Electric CITY MULTI PUHY-P108 Service Handbook page 159

[ VII Control ]
-5- Compressor Frequency Control <PUHY>
Depending on the capacity required, the frequency of the compressor is controlled to keep constant evaporation temper-
ature (0°C [32°F] = 0.71 MPa [103 psi]) during cooling operation, and condensing temperature (49°C [120°F] = 2.88 MPa
[418 psi]) during heating operation.
The capacity of the P72-P144 is controlled solely by the inverter-driven compressor, and the capacity of P168-P234 is con-
trolled by No.1 compressor (inverter) and No.2 compressor (constant capacity).
The following table shows the frequency change of the inverter compressor during normal operation.
Model
P72 model
P96 model
P108 model
P126 model
P144 model
P168 model
P192 model
P204 model
P216 model
P234 model
The maximum frequency during heating operation is affected by the outdoor air temperature to a certain extent.
(1) No. 2 compressor operation/stop (P168-P234 models only)
No.2 compressor changeover from stop to in-operation
When No.1 compressor does not meet the capacity requirement, No.2 compressor will start its operation.
No.2 compressor changeover from stop to in-operation
When an operation of both No.1 and No.2 compressors exceeds the capacity requirement, No.2 compressor will stop
its operation.
(2) Pressure limit
The maximum limit of high pressure (Pd) is set for each frequency level. If this limit is exceeded, the frequency will be
reduced every 30 seconds.
(3) Discharge temperature limit
The discharge temperature (Td) of the compressor in operation is detected, and if it exceeds the upper limit, the frequency
is reduced by 5 Hz.
Control is performed 30 seconds after compressor start-up and every 30 seconds thereafter.
Operating temperature is 115°C [239°F] .
(4) Periodic frequency control
Frequency control other than the ones performed at start-up, upon status change, and for protection is called periodic fre-
quency control (convergent control) and is performed in the following manner.
[Periodic control cycle]
Periodic control is performed after the following time has passed
30 seconds after either compressor start-up or the completion of defrost operation
30 seconds after frequency control based on discharge temperature or pressure limit
[The amount of frequency change]
The amount of frequency change is controlled to approximate the target value based on the evaporation temperature
(Te) and condensing temperature (Tc).
Frequency/cooling
20-53 Hz
20-70 Hz
20-77 Hz
20-89 Hz
20-103 Hz
20-65 Hz
20-78 Hz
20-88 Hz
20-98 Hz
20-107 Hz
- 150 -
Frequency/heating
20-59 Hz
20-85 Hz
20-98 Hz
20-102 Hz
20-103 Hz
20-73 Hz
20-84 Hz
20-93 Hz
20-105 Hz
20-113 Hz
Speed
3 Hz/second
3 Hz/second
3 Hz/second
3 Hz/second
3 Hz/second
3 Hz/second
3 Hz/second
3 Hz/second
3 Hz/second
3 Hz/second