SiUS28-902_B
Check
Service Diagnosis
147
4. Check
Check for causes of rise in high pressure
Referring to the Fault Tree Analysis (FTA) shown below, probe the error points.
Note:
1: In cooling, it is normal if the outdoor unit electronic expansion valve (EV1) is fully open.
2: In heating, the indoor unit electronic expansion valve is used for “subcooled degree control”.
CHECK 1
Short circuit
Rise in high
pressure
Local
pressure
rise
High pipe
resistance
Stop valve closed
Bent or crashed pipe
Clogging of foreign
particles
←
Check to be sure the stop valve is open.
←
Conduct visual checks for pipe conditions.
←
Is there any temperature difference caused before
and after the filter or branch pipe.
←
Are the coil resistance and insulation normal?
[In cooling]
If the outdoor unit electronic
expansion valve is throttled:
(See
∗
1.)
Defective outdoor
unit electronic
expansion valve
Defective indoor
unit electronic
expansion valve
Defective valve coil
Defective valve body
A temperature difference in excess of 50
°
F between
the inlet and the outlet is deemed to be abnormal.
Defective
control
Defective high pressure sensor
Defective service monitor PCB
←
Are the electrical characteristics normal?
←
Is the pressure value checked with the Service Checker
corresponding to the measurement of the pressure sensor?
←
Are the coil resistance and insulation
normal?
Defective high
pressure
control
Defective valve coil
Defective valve body
[In heating]
If the indoor unit electronic
expansion valve excessively
throttled:
(See
∗
2.)
Defective
control
Defective high pressure sensor
Defective indoor unit
liquid pipe thermistor
Defective service monitor PCB
←
Are the electrical characteristics normal?
←
In the connector properly connected?
Are the thermistor resistance characteristics normal?
←
Is the pressure value checked with the Service
Checker corresponding to the measurement of the
pressure sensor?
[In cooling]
High suction
air
temperature
of the
condenser
[In heating]
High suction air
temperature of
outdoor unit
Short circuit
High outdoor temperature
←
Is the suction air temperature not more than
115
°
F?
←
Is the outdoor temperature not more than 115
°
F?
High suction
air temperature
of indoor unit
High outdoor air temperature
←
Is the suction air temperature not more than 81
°
F?
←
Is the indoor temperature not more than 81
°
F?
Defective suction air thermistor of indoor unit
High suction air temperature of outdoor unit
Defective outdoor temperature thermistor of outdoor unit
←
Is the connector properly connected?
Are the thermistor resistance characteristics normal?
←
Is the outdoor temperature not more than 61˚FWB?
←
Is the connector properly connected?
Are the thermistor resistance characteristics normal?
Degradation
in condensing
capacity
Dirty condenser
Mixing of non-condensable gas
←
Is the heat exchanger clogged? (In cooling)
←
Is air or else mixed in the refrigerant system?
Decreased
fan airflow
rate
Decreased
fan
output
Defective fan
motor
←
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?
Defective service
monitor PCB
(Including
capacity setting)
High air
passage
resistance
Dirty filter
Obstacle
Excessive refrigerant charging
Improper model selection [In heating]
←
Refer to troubleshooting "F6".
←
Is the indoor unit too small compared to
the large-sized outdoor unit?
