Daikin FCQ18PVJU Service Manual page 164

Troubleshooting by Indication on the Unified ON/OFF Controller
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
If the indoor unit
(Low evaporating
temperature)
electronic
expansion valve is
throttled too much:
(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" on P.18.
*2: The "low pressure protection control" includes low pressure protection control and hot gas bypass control. For details, refer to P.30.
*3: In cooling, the indoor unit electronic expansion valve is used for "superheated degree control". (For details, refer to P.19.)
*4: In heating, the outdoor unit electronic expansion valve (EV1) is used for "superheated degree control of outdoor unit heat exchanger".
(For details, refer to P.19.)
157
[In cooling]
Faulty
(See *1.)
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
High air
rate
passage
resistance
←Are the electrical characteristics normal?
Faulty low pressure sensor
←Is the pressure value checked with the Service Checker
Faulty control P.C.B.
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 P.C.B.
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 P.C.B.
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 P.C.B.
←Is the suction air temperature not less than 57˚F
Short circuit
←Is the indoor temperature not less than 57˚F
Low ambient temperature
←Is the connector properly connected?
Are the thermistor resistance characteristics normal?
←Is the outdoor temperature not less than 5˚F
←Is the connector properly connected?
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.
←Refer to P.130.
←Eliminate moisture by vacuum operation.
←Is the heat exchanger clogged?
Faulty fan motor
Faulty control P.C.B.
(Including capacity setting)
Dirty filter
Obstacle
SiUS28-902_a
←Can the fan motor be rotated with hands?
Are the motor coil resistance and insulation normal?
←If a spare P.C.B. is mounted, is the capacity
setting properly made?
←Is the air filter clogged?
←Is there any obstacle in the air passage?
Troubleshooting