Mitsubishi Electric MXZ-8B48NA Technical & Service Manual page 58

Troubleshooting
Problem
Locked expansion
If the linear expansion valve becomes locked and the motor is still operating,
valve
the motor will emit a clicking noise and will not function. This clicking noise
indicates an abnormality.
Use an all-purpose electrical meter to measure the resistance between the
Short circuit or broken
different coils (red-white, red-orange, brown-yellow, brown-blue). Normal
circuit in expansion
resistance is within a range of 46 ± 4%.
valve motor coil
In order to check the linear expansion valve, operate 1 indoor unit in the
Valve does not close
fan mode and another in the cooling mode. Then, use the outdoor multi
completely.
controller board to operate the monitor and check the pipe temperature of
the indoor unit. The linear expansion valve should be fully closed when the
fan is operating. The temperature measured by the temperature sensor
will drop if there is any leakage.
If the measured temperature is significantly lower than that on the remote
controller, this indicates that the valve is not closed. It is not necessary to
replace the linear expansion valve if the leak of refrigerant is small and does
not cause a malfunction.
Check improperly connected connector terminals and the wire colors.
Incorrect connection
Remove the connector on the controller board side and check electrical
or connection failure
conductance.
Check point
58
Corrective measure
Replace the linear
expansion valve.
Replace the linear
expansion valve.
Replace the linear
expansion valve if there
is a major leak of
refrigerant.
Continuity check of
wrong part