MXZ-SM36NAMHZ Service Manual
71
OCH789
Check code
1508
(EF)
4-way valve trouble in heating mode
Abnormal points and detection methods Causes and checkpoints
If 4-way valve does not operate during heating operation.
When any of the following temperature conditions is satised for 3 minutes
or more during heating operation when the outdoor temperature is −4°F
[−20°C] or more:
1. TH22j − TH21j
[
−18°F [−10°C]
2. TH23j − TH21j
[
−18°F [−10°C]
3. TH22j
[
37.4°F [3
:
]
4. TH23j
[
37.4°F [3
:
]
Note:
For indoor unit, the abnormality is detected if an operating unit satises the
condition.
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)
●Diagnosis of defects
Make sure to turn the power OFF before connecting/disconnecting any connectors, or replacing boards.
Diagnosis Remedy
Is the connector for outdoor multi
controller circuit board or 4-way
valve coil disconnected or loose?
Reconnect the connector or connect it
tightly.
Yes
Disconnect the connector for outdoor multi
controller circuit board or 4-way valve coil
to check the resistance.
No
Replace the 4-way valve coil.
Replace the outdoor multi controller circuit
board.
Is the detected voltage normal?
Is it free from any trace of over-
heating or burning?
Is the resistance detected?
Check the voltage and appearance of the
outdoor multi controller circuit board.
No
No
Yes
Yes
Replace the 4-way valve.
Please refer to "8-7. HOW TO
CHECK THE PARTS" for ohm values.