Service Manual

SiUS281811E Check
Part 6 Service Diagnosis 263
Note(s)
5.3 Superheat Operation Check
CHECK 3 Referring to the Fault Tree Analysis (FTA) shown below, probe the defective points.
Abnormal piping length
Bent or crushed pipe
(Including moisture choke)
Stop valve closed.
Defective valve coil
Defective valve body
Defective valve coil
Defective valve body
←Are the coil resistance and insulation normal?
←Refer to CHECK 7 .
←Does the piping length fall in the permissible range?
←Conduct visual checks.
←Eliminate moisture by vacuum operation. (Refer to CHECK 8 .)
←Check if the stop valve is open.
Defective
discharge
pipe
temperature
control
Defective hot
gas bypass
control
Hot gas circuit clogging
Defective solenoid
valve coil
Defective solenoid
valve body
Defective service
monitor PCB
Defective main
PCB
Defective valve coil
Defective low
pressure sensor
Defective subcooling
heat exchanger outlet
thermistor
Defective valve
body
Defective
subcooling
electronic
expansion
valve control
Superheat due to
shaft damage
Superheat due to
defective compressor
Defective indoor
unit electronic
expansion valve
Defective
control
Defective
control
Defective
outdoor unit
electronic
expansion valve
Defective four
way valve
operation
[In cooling only]
(*1)
(*2)
Compressor
overheat
Refrigerant
shortage
High pipe
resistance
Defective
superheated
degree
control.
[In cooling]
If the indoor unit
electronic
expansion valve is
throttled too much:
(*3)
[In heating]
If the outdoor unit
electronic
expansion valve
excessively
throttled: (*4)
Temperature
increase of
discharge
pipe
Defective
subcooling
electronic
expansion
valve
←Are the coil resistance and
insulation normal?
←Is the connector properly connected?
Are the thermistor resistance characteristics
normal?
←Are the voltage characteristics normal?
←Is the pressure value checked with the
Service Checker corresponding to the
measurement value of the pressure sensor?
←Check if the piping temperature connected
to the four way valve is normal.
Four way valve is in the
middle position.
Leak from hot gas bypass
valve
Defective
control
Defective gas pipe
thermistor of indoor unit
Defective thermistor for
indoor unit liquid pipe
Defective main
PCB
Defective low pressure
sensor
Defective suction pipe
thermistor
Defective main
PCB
←Are the voltage characteristics normal?
←Is the pressure value checked with the Service
Checker corresponding to the measurement
value of the pressure sensor?
←Is the connector properly connected?
Are the thermistor resistance characteristics normal?
←Is the connector properly connected?
Are the thermistor resistance characteristics normal?
←Are the coil resistance and insulation normal?
←Are the coil resistance and insulation normal?
←Is the connector properly connected?
Are the thermistor resistance characteristics normal?
1: Refer to Low pressure protection control on page 87.
2: Refer to Subcooling electronic expansion valve control on page 77.
3: Superheating temperature control in cooling is conducted by indoor unit electronic
expansion valve.
4: Superheating temperature control in heating is conducted by outdoor unit electronic
expansion valve.
5: Judgment criteria of superheat operation: (1) Suction gas superheated degree: 10°C
(18°F) and over. (2) Discharge gas superheated degree: 45°C (81°F) and over, except
immediately after compressor starts up or is running under dropping control.
(Use the above values as a guide. Depending on the other conditions, the unit may be
normal despite the values within the above range.)