Mitsubishi Electric HP120TNU-A Service Handbook page 283

[8-9 Troubleshooting Problems with Major Components on BC Controller ]
Check whether the BC board output signal corresponds with the solenoid valve operation correspond.
1) SVA, SVB, SVC
SVA, SVB, and SVC turn on or off according to the indoor unit operation mode.
Port
SVM1, SVM1b
SVM1 and SVM1b turn on or off according to the indoor unit operation mode.
Operation
Cooling only
mode
SVM1,
SVM1b
2) SVA, SVB, SVC
Measure the temperature at the upstream and downstream pipes
Measure the temperature at the upstream and downstream
2
42
- chapter 8
Cooling
SVA ON
SVB OFF
SVC ON
Cooling main Heating only
Pressure dif-
ferential con-
ON
trol OFF or
ON
3
1
Mode
Heating Stopped
OFF OFF
ON OFF
OFF OFF
Heating main
OFF OFF
and of SVA.
pipes and of SVB.
Defrost Fan
OFF OFF
OFF OFF
OFF ON
Defrost Stopped
ON OFF
HWE18220_GB