MXS Service Manual

Control Specification SiUS121736EA
93 Functions and Control
4.3 Frequency Control
Outline Frequency that corresponds to each room’s capacity is determined according to the difference
between the target temperature and the temperature of each room.
Details The compressor’s frequency is determined by taking the following steps.
1. Determine command frequency
Command frequency is determined in the following order of priority.
1. Limiting defrost control time
2. Forced cooling/heating
3. Indoor frequency command
2. Determine upper limit frequency
The minimum value is set as upper limit frequency among the frequency upper limits of the
following functions:
Compressor protection, input current, discharge pipe temperature, low Hz high pressure limit,
heating peak-cut, freeze-up protection, defrost.
3. Determine lower limit frequency
The maximum value is set as the lower limit frequency among the frequency lower limits of the
following functions:
Four way valve operation compensation, draft prevention, pressure difference upkeep.
4. Determine prohibited frequency
There is a certain prohibited frequency such as a power supply frequency.
Command frequency Limit frequency
Skip control
Upper limit function
Compressor protection function
Lower limit function
Four way valve operation compensation, etc.
Target frequency
(R18023)
When the shift of the frequency is less than zero (∆F<0) by PI control,
the target frequency is used as the command frequency.
Dropping function
Input current control, etc.
Upper limit frequency
FMAX
Lower limit frequency
FMIN
Initial frequency
PI control
Defrost control