Service manual

SiUS28-902_a Troubleshooting by Indication on the Unified ON/OFF Controller
Troubleshooting 156
Check for causes of rise in high pressure
Referring to the Fault Tree Analysis (FTA) shown below, probe the faulty points.
CHECK 1
Short circuit
Rise in high
pressure
Local
pressure
rise
High pipe
resistance
Stop valve closed
Bent or crashed pipe
Clogging of foreign
¬ 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?
[In cooling]
If the outdoor unit electronic
expansion valve is throttled:
(See *1.)
Faulty outdoor
unit electronic
expansion valve
Faulty indoor
unit electronic
expansion valve
Faulty valve coil
Faulty valve body
¬ Are the coil resistance and insulation normal?
Faulty
control
Faulty high pressure sensor
Faulty control P.C.B.
¬ 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?
Faulty high
pressure
Faulty valve coil
Faulty valve body
[In heating]
If the indoor unit electronic
expansion valve excessively
throttled:
(See *2.)
Faulty
control
Faulty high pressure sensor
Faulty indoor unit
liquid pipe thermistor
Faulty control P.C.B.
¬ 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 ambient temperature
¬ Is the suction air temperature not more than
115°F?
¬ Is the outdoor temperature not more than 115°F?
High suction
air temperature
High ambient temperature
¬ Is the suction air temperature not more than 81°F?
¬ Is the indoor temperature not more than 81°F?
Faulty suction air thermistor of indoor unit
High suction air temperature of outdoor unit
Faulty 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
Faulty fan
motor
¬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?
Faulty control
P. C . B .
(Including
capacity setting)
High air
passage
resistance
Dirty filter
¬Is the air filter clogged?
Obstacle
¬Is there any obstacle in the air passage?
Excessive refrigerant charging
Improper model selection
[In heating]
¬Refer to P.112.
¬Is the indoor unit too small compared to
the large-sized outdoor unit?
*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”.
A temperature difference in excess of 50 ° F
between the inlet and the outlet is deemed abnormal.