Controlling The Heat Source Unit - Mitsubishi Electric City Multi PQHY-P72 Service Handbook

[2] Controlling the Heat Source Unit

-1- Initial Control <PQHY/PQRY>
When the power is turned on, the initial processing of the microcomputer is given top priority.
During 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 2 minutes.
During the initial processing, the LED monitor on the heat source unit's MAIN board displays S/W version -> refrigerant
type -> heat pump -> cooling only and capacity -> and communication address in turn every second.
-2- Control at Start-up <PQHY/PQRY>
The upper limit of frequency during the first 3 minutes of the operation is 50 Hz.
When the power is turned on, normal operation will start after the initial start-up mode (to be described later) has been
completed (with a restriction on the frequency).
-3- Bypass Control <PQHY/PQRY>
Bypass solenoid valves (SV1), which bypass the high- and low- pressure sides, perform the following functions.
(1) Bypass solenoid valve (SV1) (ON = Open)
Operation
At No. 1 compressor start-up, after the res-
toration of thermo, or 3 minutes after restart
During cooling or heating operation with the
compressor stopped
After the operation has stopped
During defrost operation
(See *1 in the figure below.)
During oil-recovery operation
During an operation with the compressor
running at 30 Hz (After 3 minutes have
passed since start-up)
When high pressure (Pd) rises
[Example of an SV1 operation]
Compressor
Bypass solenoid
valve (SV1)
Always OFF during cooling operation and always ON during heating op-
eration when running an oil-recovery operation after running a continuous
operation at low frequency.
When low pressure (LPS) drops
below 0.23 MPa [33 psi].
When Pd exceeds
3.77 MPa [547 psi]
Start- Thermo. Thermo.
up
OFF ON
(4-min.) (4-min.)
SV1
ON
ON for 4 minutes.
Always ON.
Exception: OFF when HPS-LPS is 0.2 MPa [29 psi] or less
ON for 3 minutes.
Exception: OFF when HPS-LPS is 0.2 MPa [29 psi] or less
Always ON
- 129 -
[ VII Control ]
OFF
When low pressure (LPS) exceeds
0.38 MPa [55 psi].
When Pd is or below
3.43 MPa [497 psi] and 30 seconds
have passed
Stopped
)
(3-min.