Hitachi UTOPIA RAS-4HVRP2E Service Manual page 218

10 Troubleshooting
Initial troubleshooting
Phenomenon
Indoor heat load is greater than the heating
Excessively low
suction pressure
Insufficient heating
process
Excessively high
discharge pressure
Malfunction or internal leakage of the 4-way
Malfunction of the check valve of the
Excessively high
suction pressure
Discharge temperature of the indoor unit is
216 SMGB0136 rev.0 - 07/2021
Cause
capacity
Gas leakage or
insufficient refrigerant
charge
Excessively small
diameter or long piping
Failure or malfunction
of the expansion valve
Clogging of IU/OU
strainer
Clogging of suction
piping
Are there any obstacles at the
Insufficient air flow
through the outdoor
unit heat exchanger
Excessively low air
temperature through
the outdoor unit heat
exchanger
Defrosting is
insufficiently
completed
Excessively charged
Check the refrigerant quantity Correctly charge the refrigerant
refrigerant
Non-condensate gas
Check the refrigerant quantity
in refrigerant cycle
Clogging of the
discharge pressure
piping
valve
outdoor unit
Malfunction or internal
leakage of 4-way valve
unstable
Check item
Calculate the heat load
Measure superheat
Measure the field supplied
piping
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 temperature
difference between the inlet
and the outlet of strainer
Check the temperature
difference of each part
Is the outdoor unit heat
exchanger clogged?
inlet or the outlet of outdoor
unit?
Is the service area for the
outdoor unit sufficient?
Check the speed of the
outdoor unit fan
Check for any short-circuited
air to the outdoor unit
Check the thermistor for the
defrost operation
Check for clogging
Check the temperature
difference at the inlet and the
outlet of the 4-way valve
Check the temperature
difference at the inlet and the
outlet of the check valve
Check the temperature
difference at the inlet and the
outlet of the 4-way valve
Check the expansion valve
of the indoor unit in the same
system
Action
(Turn OFF the main switch)
Replace the unit with a
bigger unit
Correctly charge the
refrigerant after the gas
leakage check and repairing
Use the specified pipes
Remove the clogging
Replace the connector
Replace the coil
Replace the thermistor
Correctly install the
thermistor
Replace the strainer for the
outdoor unit or the indoor unit
Remove the clogging
Remove the clogging
Remove the obstacles
Secure a sufficient service
area
Replace the fan motor
Remove the cause of the
short-circuited air
Replace the thermistor for
the defrost operation
Recharge the refrigerant after
the vacuum pumping
Remove the clogging
Replace the 4-way valve
Replace the check valve
Replace the 4-way valve
Replace the failed expansion
valve of the indoor unit