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2.18 Air return pipe forms frosts
Air return pipe forms frosts: frosting is a normal phenomenon
when the unit cools or heats the room, as the air return
temperature is below 0°C. If a thick layer of frosting forms when
the unit operates under standard condition, note to check the unit.
Block on low pressure side (such as filter, IDU electronic
expansion valve) or poor heat dissipation of IDU
evaporator (for example, evaporator or filter gets blocked,
IDU fan fails to work or only produces low air flow, or IDU
air channel has high resistance) Measure pressure on
low pressure side. If pressure is too low, the above-
mentioned circumstances may occur.
If no uniform power supply is provided, electronic expansion
valves of IDU may still remain open. Under this circumstance,
large amount of refrigerant will flow through EXV and enter air
return pipe at a very low temperature without evaporation
process.
If supplemented amount of refrigerant is too much, when
the unit operates at a low ambient temperature (cooling),
the refrigerant will enter air return pipe at a very low
temperature without evaporation process, thereby
resulting in frosting in air return pipe.
Exist
Exist
Exist
Troubleshoot
depending on the
actual conditions
All IDUs within a system
must be provided with a
uniform power supply
Discharge some refrigerant. If
refrigerant oil is discharged
together, add some refrigerant oil
OK
OK
Notes:
If the IDUs are not provided with a uniform power supply: when some IDUs are suddenly
power off, their electronic expansion valves may still remain open to let plenty of
refrigerant pass:
① but because fan does not operate, the refrigerant cannot evaporate; as a result, the
evaporator and the pipes are at a very low temperature and hence could easily generate
condensation or ices when coming in contact with indoor hot air.
② the refrigerant will return to compressor in a liquid form without evaporation process,
and may result in liquid hammer and cause harm to compressor.
③ the amount of refrigerant that passes through other normally functional IDUs is
reduced, thereby dampening cooling effects.
2.19 Sensor fault
1. THo1 sensor fault
Code displayed: ODU main board displays E008 (applicable to AA/AS/AX models).
Fault detection method: Measure resistance value of ambient temperature probe (At
25°C, resistance value is 20K. The higher the temperature, the lower the resistance value)
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