Troubleshooting for Outdoor Unit SiBE18-821_C
424 Troubleshooting
7.35.2 Check for Causes of Drop in Low Pressure
Check No.02 Referring to the Fault Tree Analysis (FTA) shown below, probe the faulty points.
Abnormally low
low-pressure
(Low evaporating
temperature)
[In cooling]
(See *1.)
Faulty low
pressure
control
Faulty
compressor
capacity
control
Faulty low pressure sensor
←
Are the electrical characteristics normal?
Faulty control PCB
←
Is the pressure value checked with the Service Checker
corresponding to the measurement of the pressure sensor?
Faulty low
pressure
protection
control
Faulty low pressure sensor
←
Are the electrical characteristics normal?
Faulty hot gas solenoid valve
←
Are the coil resistance and insulation normal?
Faulty control PCB
←
Is the pressure value checked with the Service Checker
corresponding to the measurement of the pressure sensor?
[In both cooling
and heating]
(See *2.)
[In cooling]
If the indoor unit
electronic
expansion valve is
throttled too much:
(See *3.)
Faulty
indoor unit
electronic
expansion
valve
Faulty valve coil
Faulty valve body
←Are the coil resistance and insulation normal?
Faulty
control
Faulty gas pipe
thermistor of indoor unit
Faulty liquid pipe thermistor
of indoor unit
Faulty control PCB
←
Check for the thermistor resistance and connection.
←
Check for the thermistor resistance and connection.
←
Is the pressure value checked with the Service Checker
corresponding to the measurement of the pressure sensor?
Faulty
outdoor
unit
electronic
expansion
valve
Faulty valve coil
Faulty valve body
←
Are the coil resistance and insulation
normal?
[In heating]
If the outdoor unit
electronic
expansion valve
excessively
throttled: (See *4.)
Faulty
control
Faulty low pressure sensor
Faulty suction pipe thermistor
Faulty control PCB
←
Are the electrical characteristics normal?
←
Check for the thermistor resistance and
connection.
[In cooling]
Low suction
air temperature
of the
evaporator
[In heating]
Low suction air
temperature of
indoor unit
Short-circuit
←
Is the suction air temperature not less than 14
°
C
←
Is the indoor temperature not less than 14
°
C
Low ambient temperature
Faulty suction air thermistor of indoor unit
←
Is the connector properly connected?
Are the thermistor resistance characteristics normal?
Low suction air temperature of outdoor unit
←
Is the outdoor temperature not less than -15°C
Faulty outdoor temperature thermistor of outdoor unit
←
Is the connector properly connected?
Are the thermistor resistance characteristics normal?
High pipe
resistance
Abnormal piping length
Bent or crashed pipe
Clogging of foreign particles
Stop valve closed
←
Does the piping length fall in the permissible range?
←
Conduct visual checks for pipe conditions.
←
Is there any temperature difference caused before
and after the filter or branch pipe?
←
Check to be sure the stop valve is open.
Less
circulation
quantity of
refrigerant
Degradation
in condensing
capacity
Inadequate refrigerant quantity
←Refer to troubleshooting "
U0".
Moisture choke
←Eliminate moisture by vacuum operation.
Dirty evaporator
Decreased
fan airflow
rate
Decreased
fan output
Faulty fan motor
←
Can the fan motor be rotated with hands?
Are the motor coil resistance and insulation normal?
←Is the heat exchanger clogged?
Faulty control PCB
(Including capacity setting)
←
If a spare PCB is mounted, is the capacity
setting properly made?
High air
passage
resistance
Dirty filter
←
Is there any obstacle in the air passage?
←Is the air filter clogged?
Obstacle
*1: For details of the compressor capacity control while in cooling, refer to “Compressor PI Control”.
*2: The “Low Pressure Protection Control” includes low pressure protection control and hot gas bypass control.
*3: In cooling, the indoor unit electronic expansion valve is used for “superheated degree control”. (For details, refer to
"Electronic Expansion Valve Control.)
*4: In heating, the outdoor unit electronic expansion valve (Y1E) is used for “superheated degree control of outdoor unit
heat exchanger”. (For details, refer to "Electronic Expansion Valve PI Control".)
Faulty electronic
expansion valve
control
(R13056)
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