Mitsubishi Electric PUMY-P112VKM4 Technical & Service Manual page 66

Check code
1508
(EF)
Abnormal points and detection methods
If 4-way valve does not operate during heating operation.
When any of the following temperature conditions is satisfied for 3 minutes
or more during heating operation
1. TH22j−TH21j [ −10°C [−18°F]
2. TH23j−TH21j [ −10°C [−18°F]
3. TH22j [ 3: [37.4°F]
4. TH23j [ 3: [37.4°F]
Note:
For indoor unit, the abnormality is detected if an operating unit satisfies the
condition.
●Diagnosis of defects
Make sure to turn the power OFF before connecting/disconnecting any connectors, or replacing boards.
Is the connector for outdoor multi
controller circuit board or 4-way
valve coil disconnected or loose?
Disconnect the connector for outdoor multi
controller circuit board or 4-way valve coil
to check the resistance.
Is the resistance detected?
Check the voltage and appearance of the
outdoor multi controller circuit board.
Is the detected voltage normal?
Is it free from any trace of
over-heating or burning?
OCH673C
4-way valve trouble in heating mode
Diagnosis
No
Yes
Yes
Causes and checkpoints
4-way valve failure
Disconnection or failure of 4-way valve coil
Clogged drain pipe
Disconnection or loose connection of connectors
Malfunction of input circuit on outdoor multi controller circuit board
Defective outdoor power circuit board
Reconnect the connector or connect it
Yes
tightly.
No
Replace the outdoor multi controller circuit
No
board.
Replace the outdoor multi controller circuit
board.
66
Remedy
Replace the 4-way valve.