Mitsubishi Electric CMB-WM108V-AA Service Handbook page 190

[ VIII Troubleshooting ]
2. HBC controller LEV1 and 2 actuation failure
Sufficient hot water is not supplied on the HBC con-
troller due to HBC controller LEVI, 2, and 3 actuation
failure.
3. Temperature reading error on the indoor unit piping
temperature sensor
If the temperature reading on the sensor is higher
than the actual temperature, it makes the subcool
seem smaller than it is, and the LEV opening de-
creases too much.
4 RPM error of the outdoor unit FAN
Motor failure or board failure, or airflow rate de-
crease, pressure drop due to clogging of the heat
exchanger leading to high discharge temperature
The fan is not properly controlled as the tempera-
ture cannot be precisely detected with the piping
sensor.
5. Insulation failure of the refrigerant piping
6. Long piping length
Excessively long piping on the high pressure side
causes pressure loss leading to increase in the high
pressure.
7. Piping size is not proper (thin)
8. Clogging by foreign object
9. The indoor unit inlet temperature is excessively
high.(exceeding 28°C [82°F])
10. Insufficient refrigerant amount
Protection works and compressor frequency does
not rise due to low discharge temperature
Refrigerant recovery operation is likely to start.
11. Compressor failure (same as in case of cooling)
12. HBC controller LEV3 actuation failure
A drop in the low pressure that is caused either by a
blockage of liquid pipe or by a pressure loss and the
resultant slowing of refrigerant flow causes a tenden-
cy for the discharge temperature to rise.
13. HBC controller valve block actuation failure
Sufficient hot water is not supplied because of the in-
sufficient water flow rate and coexistence of cold and
hot water on the HBC controller due to valve block
actuation failure.
HWE1708A
Cause Check method and remedy
Refer to the page of LEV troubleshooting ([4] -1-).
(page 186)
Check the thermistor.
Refer to the page on outdoor unit fan in outdoor unit
service handbook
Confirm that the characteristic of capacity drop due
to piping length.
-> Change the pipe
Check the temperature difference between the up-
stream and the downstream of the pipe section that
is blocked. Since blockage in the extended section
is difficult to locate, operate the unit in the cooling
cycle, and follow the same procedures that are
used to locate the blockage of pipe during cooling
operation.
->Remove the blockage in the pipe.
Check the inlet air temperature and for short cy-
cling. Change the environment where the indoor
unit is used.
Refer to 2 - 1. (Compressor frequency does not rise
sufficiently.)(page 180)
Refer to the page on refrigerant amount
adjustment.(page 124)
Check the discharge temperature.
Refer to the page of LEV troubleshooting ([4] -1-).
(page 186)
Refer to the section on valve block fault under
"Troubleshooting." (page 200)
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