Low Pressure Check - Daikin RXYQ-TA Series Service Manual

SiUS341615E
4.2

Low Pressure Check

CHECK 2
Referring to the Fault Tree Analysis (FTA) shown below, probe the defective points.
Abnormally drooping
low pressure
(Low evaporating
temperature)
∗1. For details of compressor capacity control while in cooling.
Note:
∗2. The "low pressure protection control" includes low pressure protection control and hot gas
∗3. In cooling, the indoor unit electronic expansion valve is used for "superheated degree control".
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
In cooling
Low suction air
temperature of
indoor unit
Low suction air
Defective suction air thermistor of indoor unit
temperature of
the evaporator
High pipe
resistance
Less
circulation
Refrigerant shortage
quantity of
refrigerant
Moisture choke
Dirty
evaporator
Degradation
in condensing
capacity
Decreased
airflow rate
bypass control.
Defective low pressure
←Are the electrical characteristics normal?
sensor
←Is the pressure value checked with the Service Checker
Defective outdoor
unit main PCB
corresponding to the measurement value of the pressure sensor?
Defective low pressure
←Are the electrical characteristics normal?
sensor
Defective hot gas ←Are the coil resistance and insulation normal?
solenoid valve
←Is the pressure value checked with the Service Checker
Defective outdoor
unit main PCB
corresponding to the measurement value of the pressure sensor?
←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
←Is the pressure value checked with the Service Checker
Defective outdoor
unit main PCB
corresponding to the measurement value of the pressure sensor?
←Is the suction air temperature more 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?
←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 materials
and after the filter or branch pipe?
Stop valve closed
←Refer to
CHECK 7
←Eliminate moisture by vacuum operation.
←Is the heat exchanger clogged?
Defective fan motor
Decreased
fan output
Defective outdoor unit main
PCB (Including capacity setting)
High
airflow
Dirty filter
passage
resistance
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 airflow passage?
Check
292