4-Way Valve Trouble In Heating Mode - Mitsubishi Electric PUMY-P250YBM Technical & Service Manual

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°C [37.4°F]
4. TH23j [ 3°C [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?
OCH760

4-way valve trouble in heating mode

Diagnosis
No
Please refer to "8-6. HOW TO
CHECK THE PARTS" for ohm values.
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
TH21: Indoor intake temperature thermistor (RT11 or TH1)
TH22: Indoor liquid pipe temperature thermistor (RT13 or TH2)
TH23: Indoor gas pipe temperature thermistor (TH-A to E)
Reconnect the connector or connect it
Yes
tightly.
No
Replace the 4-way valve coil.
Replace the outdoor multi controller circuit
No
board.
Replace the 4-way valve.
55
Remedy