Daikin RXYQ96PYDN Service Manual page 478

SiUS34-801A_b
[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)
*1: The "low pressure protection control" includes low pressure protection control and hot gas bypass control. For details, refer to P66, 213.
*2: In cooling, the indoor unit electronic expansion valve is used for "superheated degree control".
*3: In heating, the outdoor unit electronic expansion valve (EVM) is used for "superheated degree control of outdoor unit heat exchanger".
Troubleshooting
[In cooling]
Faulty
(See *1.)
compressor
Faulty low
capacity
pressure
control
control
Faulty low
pressure
protection
[In both cooling
control
and heating]
(See *2.)
Faulty indoor
[In cooling]
unit electronic
If the indoor unit
expansion valve
electronic
expansion valve is
throttled too much:
(See *3.)
Faulty
control
Faulty electronic
expansion valve
control
Faulty outdoor
unit electronic
expansion valve
[In heating]
If the outdoor unit
electronic
expansion valve Faulty
excessively
control
throttled:
(See *4.)
[In cooling]
Low suction air
temperature of
indoor unit
Low suction
Faulty suction air thermistor of indoor unit
air temperature
of the
evaporator
Low suction air temperature of outdoor unit
Faulty outdoor temperature thermistor of outdoor unit
[In heating]
High pipe
resistance
Less
circulation
Inadequate refrigerant quantity
quantity of
refrigerant
Moisture choke
Dirty
evaporator
Degradation
in condensing
capacity
Decreased
fan airflow
rate
(For details, refer to P47, 195.)
Troubleshooting (OP: Unified ON/OFF Controller)
←Are the electrical characteristics normal?
Faulty low pressure sensor
←Is the pressure value checked with the Service Checker
Faulty control PC board
corresponding to the measurement of the pressure sensor?
←Are the electrical characteristics normal?
Faulty low pressure sensor
←Are the coil resistance and insulation normal?
Faulty hot gas solenoid valve
←Is the pressure value checked with the Service Checker
Faulty control PC board
corresponding to the measurement of the pressure sensor?
←Are the coil resistance and insulation normal?
Faulty valve coil
Faulty valve body
←Check for the thermistor resistance and connection.
Faulty gas pipe
thermistor of indoor unit
←Check for the thermistor resistance and connection.
Faulty liquid pipe thermistor
of indoor unit
←Is the pressure value checked with the Service Checker
Faulty control PC board
corresponding to the measurement of the pressure sensor?
←Are the coil resistance and insulation
Faulty valve coil
normal?
Faulty valve body
←Are the electrical characteristics normal?
Faulty low pressure sensor
Faulty suction pipe thermistor ←Check for the thermistor resistance and
connection.
Faulty control PC board
←Is the suction air temperature not less than 57.2˚F
Short circuit
←Is the indoor temperature not more than 57.2˚F
Low ambient temperature
←Is the connector properly connected?
Are the thermistor resistance characteristics normal?
←Is the outdoor temperature not less than -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
Clogging of foreign particles
and after the filter or branch pipe?
Stop valve closed
←Refer to P414.
←Eliminate moisture by vacuum operation.
←Is the heat exchanger clogged?
Faulty fan motor
Decreased
fan output
Faulty control PC board
(Including capacity setting)
High air
passage
Dirty filter
resistance
Obstacle
←Can the fan motor be rotated with hands?
Are the motor coil resistance and insulation normal?
←If a spare PC board is mounted, is the capacity
setting properly made?
←Is the air filter clogged?
←Is there any obstacle in the air passage?
SDK04009
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