Low Pressure Check - Daikin VRV RXYQ72-384XAYCA Service Manual

SiUS342004EB
4.2

Low Pressure Check

CHECK 2
Referring to the Fault Tree Analysis (FTA) shown below, probe the defective points
Abnormal drop in
[In cooling]
low pressure
If the indoor unit
(Low evaporating
temperature) electronic
expansion valve is
excessively
throttled: (3.)
[In heating]
If the outdoor unit
electronic
expansion valve
is excessively
throttled:
(4.)
Note(s)
1. For details of 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
3. In cooling, the indoor unit electronic expansion valve is used for superheating degree control.
4. In heating, the outdoor unit electronic expansion valve (main) is used for superheating
Part 6 Service Diagnosis
[In cooling]
(1.)
Defective
compressor
Defective
capacity
low pressure
control
control
[In both cooling
Defective
low pressure
and heating]
protection
(2.)
control
Defective indoor
unit electronic
expansion valve
Defective
control
Defective electronic
expansion valve
control
Defective outdoor
unit electronic
expansion valve
Defective
control
[In cooling]
Low suction air
temperature of
indoor unit
Low suction air
Defective suction air thermistor of indoor unit
temperature of
the evaporator
Low suction air temperature of outdoor unit
Defective outdoor air temperature thermistor of outdoor unit
[In heating]
High pipe
resistance
Less
circulation
Refrigerant shortage
quantity of
refrigerant
Moisture choke
Dirty
evaporator
Degradation
in evaporating
capacity
Decreased
airflow rate
bypass control.
degree control of outdoor heat exchanger.
Defective low pressure
Is the pressure value checked with the Service Checker
sensor
corresponding to the measurement value of the pressure sensor?
Defective outdoor unit
Are the voltage characteristics normal?
main PCB
Is the pressure value checked with the Service Checker
Defective low pressure
sensor
corresponding to the measurement value of the pressure sensor?
Defective hot gas
Are the coil resistance and insulation normal?
solenoid valve
Defective outdoor unit
Are the voltage characteristics normal?
main PCB
Are the coil resistance and insulation normal?
Defective valve coil
Defective valve body
Defective gas pipe
Check for the thermistor resistance and connection.
thermistor of indoor unit
Defective liquid pipe
Check for the thermistor resistance and connection.
thermistor of indoor unit
Defective outdoor unit
Are the voltage characteristics normal?
main PCB
Are the coil resistance and insulation normal?
Defective valve coil
Defective valve body
Defective low pressure
Is the pressure value checked with the Service Checker
sensor
corresponding to the measurement value of the pressure sensor?
Defective suction pipe
Check for the thermistor resistance and connection.
thermistor
Defective outdoor unit
main PCB
Short circuit
Is the suction air temperature more than 14°C (57.2°F)?
Low room temperature
Is the room temperature less than 14°C (57.2°F)?
Is the connector properly connected?
Are the thermistor resistance characteristics normal?
Is the outdoor air temperature more than –20°C (–4°F)?
Is the connector properly connected?
Are the thermistor resistance characteristics normal?
Abnormal piping length
Does the piping length fall in the permissible range?
Bent or crashed pipe
Conduct visual checks for pipe conditions.
Clogging of foreign materials Is there any temperature difference caused before
and after the filter or branch pipe?
Stop valve closed
Check if the stop valve is open.
Refer to CHECK 7.
Eliminate moisture by vacuum operation. (Refer to CHECK 8)
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
358