Hitachi RASC-4HNPE Service Manual page 201

10 Troubleshooting
Initial troubleshooting
Phenomenon
Insufficient cooling process
191 SMGB0091 rev.2 - 11/2015
Cause
Indoor cool load is greater than the
cooling capacity
Gas leakage
or shortage of
refrigerant
Excessively
small diameter
tube or long
piping
Incorrect
activation of the
check valve of
the RASC unit
Failure or
malfunction of
the expansion
valve
Excessively low
suction pressure
Clogged strainer
in the indoor
unit; clogging at
the low pressure
piping
Clogging at the
low pressure
piping
Insufficient
air flow to the
indoor unit heat
exchanger
Excessively low
air temp. to the
indoor unit heat
exchanger
Check item
Calculate the cool load
Measure superheat
Measure and check the field-
supplied pipes
Check whether or not the
temperature difference exists
before/after the check valve
Check for clogging
Check the connection cord
and the connector
Is there an operation sound
from the coil?
Is the thermistor on the
compressor normal?
Is the thermistor installed
correctly on compressor?
Check the temp. difference at
the inlet and the outlet of the
strainer
Check the temperature
difference
Check for clogged air filter
Check for an obstacle at the
inlet or the outlet
Insufficient speed of the
indoor unit fan motor?
Short-circuited indoor unit
air?
Action
(Turn OFF the main switch)
Use a bigger unit
Correctly charge the refrigerant
after repairing the gas leakage
Use the correct pipes
Replace the check valve for
the RASC unit
Remove the clogging
Replace the connector
Replace the coil
Replace the thermistor
Correctly install the thermistor
Replace the strainer in the
indoor unit
Remove the clogging
Clean the air filter
Remove the obstacles
Replace the fan motor
Remove the cause of the
short-circuited air
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