Table of Contents
SiUS341802E
3.2
Low Pressure Check
CHECK 2
Referring to the Fault Tree Analysis (FTA) shown below, probe the defective points.
Abnormally dropin
low pressure
(Low evaporating
temperature)
∗1: For details of compressor capacity control while in cooling, refer to Compressor PI control.
Notes:
∗2: The low pressure protection control includes low pressure protection control and hot gas bypass
∗3: In cooling, the indoor unit electronic expansion valve is used for superheated degree control.
∗4: In heating, the outdoor unit electronic expansion valve is used for superheated degree control of
Service Diagnosis
[In cooling]
Defective
(∗1.)
compressor
Defective
capacity
low pressure
control
control
Defective
low pressure
protection
[In both cooling
control
and heating]
(∗2.)
Defective indoor
[In cooling]
unit electronic
If the indoor unit
expansion valve
electronic
expansion valve is
throttled too much:
(∗3.)
Defective
control
Defective electronic
expansion valve
control
Defective outdoor
unit electronic
expansion valve
[In heating]
If the outdoor unit
electronic
expansion valve
Defective
excessively
control
throttled:
(∗4.)
[In cooling]
Low suction air
temperature of
indoor unit
Low suction air
Defective suction air thermistor of indoor unit
temperature of
the evaporator
Low suction air temperature of outdoor unit
Defective outdoor air temperature thermistor of outdoor unit
[In heating]
High pipe
resistance
Less
circulation
Refrigerant shortage
quantity of
refrigerant
Moisture choke
Dirty
evaporator
Degradation
in evaporating
capacity
Decreased
airflow rate
control.
outdoor unit heat exchanger.
Defective low pressure
←Is the pressure value checked with the Service Checker
sensor
corresponding to the measurement value of the pressure sensor?
←Are the voltage characteristics normal?
Defective main PCB
←Is the pressure value checked with the Service Checker
Defective low pressure
sensor
corresponding to the measurement value of the pressure sensor?
Defective hot gas
←Are the coil resistance and insulation normal?
solenoid valve
←Are the voltage characteristics normal?
Defective main PCB
←Are the coil resistance and insulation normal?
Defective valve coil
Defective valve body
←Check for the thermistor resistance and connection.
Defective gas pipe
thermistor of indoor unit
←Check for the thermistor resistance and connection.
Defective liquid pipe
thermistor of indoor unit
←Are the voltage characteristics normal?
Defective main PCB
←Are the coil resistance and insulation normal?
Defective valve coil
Defective valve body
←Is the pressure value checked with the Service Checker
Defective low pressure
sensor
corresponding to the measurement value of the pressure sensor?
Defective suction pipe
←Check for the thermistor resistance and connection.
thermistor
Defective main PCB
←Is the suction air temperature less than 14˚C (57.2˚F)?
Short circuit
←Is the room temperature less than 14˚C (57.2˚F)?
Low room temperature
←Is the connector properly connected?
Are the thermistor resistance characteristics normal?
←Is the outdoor air temperature less than –20˚C (–4˚F)?
←Is the connector properly connected?
Are the thermistor resistance characteristics normal?
←Does the piping length fall in the permissible range?
Abnormal piping length
←Conduct visual checks for pipe conditions.
Bent or crashed pipe
←Is there any temperature difference caused before and
Clogging of foreign materials
after the filter or branch pipe?
Stop valve closed
←Refer to the
CHECK 7
←Eliminate moisture by vacuum operation. (Refer to
←Is the heat exchanger clogged?
Defective fan motor
Decreased
fan output
Defective main PCB
(Including capacity setting)
High
airflow
Dirty filter
passage
resistance
Obstacle
.
CHECK 8
←Can the fan motor be rotated with hands?
Are the motor coil resistance and insulation normal?
←If a spare PCB is installed, is the
capacity setting properly made?
←Is the air filter clogged?
←Is there any obstacle in the airflow passage?
Check
)
284
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Troubleshooting
