4-Way Valve Trouble In Heating Mode - Mitsubishi Electric PUMY-P200YKM Technical & Service Manual

Check code
1508
Abnormal points and detection methods
Abnormal if 4-way valve does not operate during heating operation.
Abnormal when any of the following temperature conditions is satisfied for
3 min. or more during heating operation
1. TH22j−TH21j [ −10°C [14-F]
2. TH23j−TH21j [ −10°C [14-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 defectives
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 there a 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
OCH575

4-way valve trouble in heating mode

Diagnosis
No
Yes
or burning?
Causes and check points
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
TH22: Indoor liquid pipe temperature thermistor
TH23: Indoor gas pipe temperature thermistor
Reconnect the connector or connect it
Yes
tightly.
No
Replace the outdoor multi controller circuit
No
board.
44
Remedy
Replace the 4-way valve.