Mitsubishi Electric PUMY-P36NKMU4 Technical & Service Manual page 69

Check code
Freeze protection of Branch box or Indoor unit
1503
(P6)
Abnormal points and detection methods
The purpose of the check code is to prevent indoor unit from freezing or
dew condensation which is caused when a refrigerant keeps flowing into
the unit in STOP.
When all of the following conditions are satisfied:
1. The compressor is operating in COOL mode.
2. 15 minutes have passed after the startup of the compressor, or the
change in the number of operating indoor units is made (including a
change by turning thermo-ON/OFF).
3. After the condition 2 above is satisfied, the thermistor of indoor unit
in STOP detects TH22j ≤ 23°F [−5°C] for 5 consecutive minutes.
●Diagnosis of defects
Make sure to turn the power OFF before connecting/disconnecting any connectors, or replacing boards.
Check the port which the piping and
wiring between the indoor unit and
branch box is connected.
Is the piping and wiring connected to the
same port?
Check the port which the LEV wiring of
branch box is connected.
Is the wiring connected to the same port as
the corresponding branch box?
Check the LEV wiring of indoor unit that is not
via branch box is connected properly.
Disconnect the LEV wiring of branch box or indoor
unit to check the resistance.
Is the resistance detected?
OCH811A
Diagnosis
Yes
Yes
v
Yes
Yes
Causes and checkpoints
Wrong piping connection between indoor unit and
1
branch box
Miswiring between indoor unit and branch box
2
3 Miswiring of LEV in branch box
Malfunction of LEV in branch box
LEV: Linear expansion valve
TH22: Indoor liquid pipe temperature thermistor
Connect the piping and wiring to the same
No
port.
Connect the LEV wiring to the intended
No
port properly.
Connect the LEV wiring properly.
No
No
Replace the LEV assy in branch box or
the LEV of indoor unit that is not
via branch box.
69
Remedy
Replace the LEV coil.