Mitsubishi Electric PQHY-P72ZLMU-A Service Handbook page 331

[ IX Troubleshooting ]
-3- Solenoid Valve
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.
SW4 (SW6-10:OFF)
SW4
ON
2 3 4 5 6 7 8 9 10
1
SW4
ON
1 2 3 4 5 6 7 8 9 10
ON
1 2 3 4 5 6 7 8 9 10
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 (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 complete 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 separator 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 - 4d, SV7a, 7b(Controls heat exchanger capacity)
1) At least one of the solenoid valves among SV4a through 4d,SV7a, and SV7b turns on. Check for proper operation on the LED
and by listening for the operation sound of the solenoid valve.
2) SV4a, 4b, 4c, 4d, 7a, and 7b control the flow of high-temperature (high-pressure) refrigerant during Cooling-only and Cooling-
main operation. These valves will be closed during the Heating-only and Heating-main operation and will not allow the refrig-
erant to flow.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 water inlet 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.
HWE15150
LD1 LD2
Upper 21S4a
Lower
Upper SV4a SV4b
Lower SV7a SV7b
The figure at left shows that the switches 1 through 5 are set to ON and 6 through 10 are set to OFF.
Display
LD3 LD4 LD5
CH11 SV1a
21S4b
SV7c
- 322 -
LD6 LD7 LD8
SV4d SV9
GB