Daikin RQYQ140-180PY1 Service Manual page 199

SiBE341001
CHECK 2
Check for causes of drop in low pressure
Referring to the Fault Tree Analysis (FTA) shown below, probe the faulty points.
Faulty low
pressure
control
[In both cooling
and heating]
(See *2.)
Abnormally low
[In cooling]
low-pressure (Low
If the indoor unit
evaporating
temperature)
electronic
expansion valve is
excessively
throttled: (See *3.)
Faulty electronic
expansion valve
control
[In heating]
If the outdoor unit
electronic
expansion valve
excessively
throttled:
(See *4.)
[In cooling]
Low suction
air
temperature
of the
evaporator
[In heating]
Less
circulation
quantity of
refrigerant
Degradation
in condensing
capacity
*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".
*4: In heating, the outdoor unit electronic expansion valve (EVM) is used for "superheated degree control of
outdoor unit heat exchanger".
Troubleshooting
[In cooling]
(See *1.)
Faulty
compressor
capacity
control
Faulty low
pressure
protection control
Faulty indoor unit
electronic
expansion valve
Faulty
control
Faulty outdoor
unit electronic
expansion valve
Faulty
control
Low suction air
temperature of
indoor unit
Faulty suction air thermistor of indoor unit
Low suction air temperature of outdoor unit
Faulty outdoor temperature thermistor of outdoor unit
Abnormal piping length
High pipe
Bent or crashed pipe
resistance
Clogging of foreign particles
Stop valve closed
Inadequate refrigerant quantity
Moisture choke
Dirty evaporator
Decreased
fan output
Decreased
fan airflow
rate
High air
passage
resistance
Troubleshooting by Remote Controller
←
Are the electrical characteristics normal?
Faulty low pressure sensor
← ←
Is the pressure value checked with the Service Checker Is the pressure value checked with the Service Checker
Faulty control PCB
corresponding to the measurement of the pressure sensor? corresponding to the measurement of the pressure sensor?
Faulty low pressure sensor ←
Are the electrical characteristics normal?
←
Are the coil resistance and insulation normal?
Faulty hot gas solenoid valve
←
Is the pressure value checked with the Service Checker
Faulty control PCB
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
Faulty gas pipe
connection.
thermistor of indoor unit
←
Check for the thermistor resistance and
Faulty liquid pipe thermistor
connection.
of indoor unit
←
Is the pressure value checked with the Service Checker
Faulty control PCB
corresponding to the measurement of the pressure sensor?
←
Are the coil resistance and insulation normal?
Faulty valve coil
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 PCB
←
Is the suction air temperature not less than 14°C
Short circuit
←
Is the indoor temperature not more than 14°C
Low ambient temperature
←
Is the connector properly connected?
Are the thermistor resistance characteristics normal?
←
Is the outdoor temperature more than -20°C
← ←
Is the connector properly connected? Is the connector properly connected?
Are the thermistor resistance characteristics normal? Are the thermistor resistance characteristics normal?
←
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.
←
Eliminate moisture by vacuum operation.
←
Is the heat exchanger clogged?
Faulty fan motor
Faulty control PCB
(Including capacity setting)
Dirty filter
Obstacle
←
Can the fan motor be rotated with hands?
Are the motor coil resistance and insulation normal?
←
If a spare PCB is mounted, is the
capacity setting properly made?
←
Is the air filter clogged?
←
Is there any obstacle in the air passage?
190