Controlling The Heat Source Unit - Mitsubishi Electric PQHY-P72TYHMU-A Service Handbook

[ VII Control ]

[2] Controlling the Heat source Unit

-1- Outline of Control Method
ŒThe heat source units are designated as OC and OS in the order of capacity from large to small (if two or more units have the
same capacity, in the order of address from small to large).
ŒThe setting of heat source unit can be verified by using the self-diagnosis switch (SW1).
SW1
1 2 3 4 5 6 7 8 9 1 0
ON
ŒThe OC determines the operation mode and the control mode, and it also communicates with the indoor units.
ŒThe OS exercises autonomous distributed control (over defrost, error detection, and actuator control etc.) according to the
operation/control mode signals that are sent from the OC.
-2- Startup sequence rotation
ŒAt the initial startup, heat source units start up in the order of "OC and OS."
ŒStartup sequence rotation is performed while all the indoor units are stopped. (Even after two hours of operation, startup se-
quence rotation is not performed while the compressor is in operation.)
In a system with multiple heat source units (OC and OS), when the integrated operation time of the unit in operation (either
OC or OS) reaches one hour during a cooling operation at low outside temperature, that unit will stop and the other unit will
go into operation.
ŒRefer to [-13-Control at Initial Start-up] for the initial startup.
ŒPerforming startup sequence rotation does not change the basic operation of OC and OS. Only startup sequence is changed.
ŒStartup sequence of the heat source units can be checked with the self-diagnosis switch (SW1) on the OC.
SW1
1 2 3 4 5 6 7 8 9 1 0
ON
-3- Initial Control
ŒWhen the power is turned on, the initial processing of the microcomputer is given top priority.
ŒDuring the initial processing, control processing of the operation signal is suspended. (The control processing is resumed after
the initial processing is completed. Initial processing involves data processing in the microcomputer and initial setting of each
of the LEV opening. This process will take up to 5 minutes.)
ŒDuring the initial processing, the LED monitor on the heat source unit's control board displays S/W version -> refrigerant type
-> heat pump -> cooling only and capacity -> and communication address in turn every second.
-4- Control at Start-up
ŒThe upper limit of frequency during the first 3 minutes of the operation is 50 Hz.
ŒWhen the power is turned on, normal operation will start after the initial start-up mode (to be described later) has been com-
pleted (with a restriction on the frequency).
HWE09080
Display
The unit is designated as the OC: "oc" appears on the display.
The unit is designated as OS: "oS" appears on the display
OC→OS: "oc" and the "OC" address appear alternately on the display.
OS→OC: "oS" and the "OS" address appear alternately on the display.
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Display
GB