Mitsubishi Electric CITY MULTI PUHY-P108 Service Handbook page 158

-4- Bypass Control <PURY>
Bypass solenoid valves (P72-P144,SV1, SV2; P168-P234,SV1, SV2, SV3), 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 or at No. 2
compressor start-up
(P168-P234 models only)
After going from Thermo-OFF condition to
Thermo-ON condition or after 3-minutes re-
start prevention
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)
(2) Bypass solenoid valve (SV2) (ON = Open)
Operation
When low pressure (LPS) drops in
heating-only mode or heating-main mode
(after 5 minutes since the compressor
start-up)
(3) Bypass valve (SV3, P168-P234 models only) (ON = Open)
The opening of SV3 depends on the operating state of No.1 and No.2 compressors.
No.1 Compressor
Stopped
In operation
In operation
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.) (2-min.)
When low pressure (LPS) drops
below 0.25 MPa [36 psi].
No.2 Compressor
Stopped
Stopped
In operation
SV1
ON
ON for 4 minutes.
ON for 2 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
Defrost
time
(*1)
(8-min.)
SV2
ON
SV3
OFF
ON
OFF
- 149 -
[ 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.
OFF
When low pressure (LPS) exceeds
0.39 MPa [57 psi].