Specifications

Troubleshooting (OP: Unified ON/OFF Controller) Si34-704
308 Troubleshooting
[CHECK 6] Check for causes of drop in low pressure
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 more 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 -20˚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 page 264.
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” on page 86.
*2: The “low pressure protection control” includes low pressure protection control and hot gas bypass control. For details, refer to page 106.
*3: In cooling, the indoor unit electronic expansion valve is used for “superheated degree control”. (For details, refer to page 121.)
Faulty electronic
expansion valve
control
SDK04009