Mitsubishi Electric R410A Service Handbook page 265

[8-6 Troubleshooting Solenoid Valve Problems ]
(3) In case of SV1a (Bypass valve)
This solenoid valve opens when powered (Relay ON).
1) At compressor start-up, the SV1a turns on for 4 minutes, and the operation can be checked by the self-diagnosis LED display
and the closing sound.
2) To check whether the valve is open or closed, check the change of the SV1a downstream piping temperature while the valve
is being powered.Even when the valve is closed, high-temperature refrigerant flows inside the capillary next to the valve.
(Therefore, temperature of the downstream piping will not be low with the valve closed.)
(4) In the case of SV5b (Solenoid valve) (SV5b is present only on the P120, P144, and P168 models.)
This solenoid valve is a switching valve that opens when energized. If checking by listening to the sound is difficult because
SV5b is switched at the same time as 21S4b during cooling, you can check whether or not the refrigerant is flowing by the
temperature of the pipes before and after.
(5) In the case of SV9 (Solenoid valve)
This solenoid valve is a switching valve that opens when energized. Proper operation of this valve can be checked on the LED
display and by the switching sound.
(6) In the case of SV2 (Solenoid valve)
This solenoid valve is a switching valve that opens when energized. Proper operation of this valve can be checked on the LED
display and by the switching sound.
Do not give an impact from outside, as the outer hull will be deformed leading to the malfunction of the inner valve.
HWE14080 - 256 - GB