Mitsubishi Electric PURY-EP200YLM-A, Service Handbook, Page: 326 / 434

[8-6 Troubleshooting Solenoid Valve Problems ]
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8-6 Troubleshooting Solenoid Valve Problems
Check whether the output signal from the control board and the operation of the solenoid valve match.
Setting the self-diagnosis switch (SW4) as shown in the figure below causes the ON signal of each relay to be output to the LED's.
Each LED shows whether the relays for the following parts are ON or OFF. LEDs light up when relays are on.
The circuits on some parts are closed when the relays are ON. Refer to the following instructions.

For how to read the SW settings, refer to the following page(s). [9-1-1 How to Read the LED](page 385)
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When a valve malfunctions, check if the wrong solenoid valve coil is not attached the lead wire of the coil is not disconnected,
the connector on the board is not inserted wrongly, or the wire for the connector is not disconnected.
(1) In case of 21S4a, 21S4b (4-way switching valve)
About this 4-way valve
When not powered:
Conducts electricity between the oil separator outlet and heat exchanger AND the gas ball valve (BV1) and the accumulator to com-
plete the circuit for the cooling cycle.
When powered:
The electricity runs between the oil separator and the gas ball valve, and between the heat exchanger and the accumulator. This
circulation is for heating.
Check the LED display and the intake and the discharge temperature for the 4-way valve to check whether the valve has no faults
and the electricity runs between where and where.Do not touch the pipe when checking the temperature, as the pipe on the oil sep-
arator side will be hot.
Do not give an impact from outside, as the outer hull will be deformed leading to the malfunction of the inner valve.
(2) 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.)
(3) SV4a, 4b and 4d (P200, P250, P300, P350, P400, EP200, EP250, EP300, EP350models), SV4a - 4d (P450, P500, EP400,
EP450, EP500models)(Controls heat exchanger capacity)
1) Depending on the conditions during Cooling-only operation, at least one of the solenoid valves among SV4a through 4d turns
on. Check for proper operation on the LED and by listening for the operation sound of the solenoid valve.
2) During Heating-only operation, SV4a through 4d all turn on. Check for proper operation on the LED and by listening for the
operation sound of the solenoid valves.
3) Depending on the conditions during Cooling-main or Heating-main operation, at least one of the solenoid valves among SV4a
through 4d turns on. Check for proper operation on the LED and by listening for the operation sound of the solenoid valve.
4) The diagram on the next page shows the refrigerant flow. This diagram shows the flow of the high-temperature (high-pressure)
gas refrigerant in the Cooling-only and Cooling-main modes and the flow of the low-temperature gas/liquid refrigerant in the
Heating-only and Heating-main modes. Refer to the refrigerant circuit diagram. Solenoid valves turns on and off according to
such factors as the capacity of the indoor units in operation and outside temperature. Check the LED. Remove the SV coil,
open the lid, and check the plunger. The type of pin face wrench that is listed in the service parts list is required to perform
this task.
SW4 (SW6-10:OFF)
Display
LD1 LD2 LD3 LD4 LD5 LD6 LD7 LD8
Upper 21S4a SV10 CH11 SV1a SV11
Lower 21S4b SV5b
Upper SV4a SV4b SV4c SV4d SV9
Lower SV7
ON
SW4
1 2 3 4 5 6 7 8 9 10 OFF
ON
SW4
1 2 3 4 5 6 7 8 9 10 OFF