Hitachi RAS-10HRNM, Service Manual, Page: 210 / 482

Phenomenon Cause Check item
Action
(Turn OFF the main switch)
Insufficient heating
process
Indoor heat load is greater than the heating capacity Calculate the heat load Replace the unit with a bigger unit
Excessively low suction
pressure
Gas leakage or
insufficient refrigerant
charge
Measure superheat
Correctly charge the refrigerant
after the gas leakage check and
repairing
Excessively small
diameter or long piping
Measure the field supplied piping Use the specified pipes
Failure or malfunction of
the expansion valve
Check for clogging Remove the clogging
Check the connection cord and
the connector
Replace the connector
Is there an operation sound from
the coil?
Replace the coil
Is the thermistor on the
compressor normal?
Replace the thermistor
Is the thermistor installed
correctly on compressor?
Correctly install the thermistor
Clogging of I.U./O.U.
strainer
Check the temp. difference
between the inlet and the outlet
of strainer
Replace the strainer for the
outdoor unit or the indoor unit
Clogging of suction
piping
Check the temp. difference of
each part
Remove the clogging
Insufficient air flow
through the outdoor unit
heat exchanger
Is the outdoor unit heat
exchanger clogged?
Remove the clogging
Are there any obstacles at the
inlet or the outlet of outdoor unit?
Remove the obstacles
Is the service area for the
outdoor unit sufficient?
Secure a sufficient service area
Check the speed of the outdoor
unit fan
Replace the fan motor
Excessively low air
temp. through the
outdoor unit heat
exchanger
Check for any short-circuited air
to the outdoor unit
Remove the cause of the short-
circuited air
Defrosting is
insufficiently completed
Check the thermistor for the
defrost operation
Replace the thermistor for the
defrost operation
Excessively high
discharge pressure
Insufficient air flow to the
indoor unit heat
exchanger
Check the filter for a clogging Remove the clogging
Check for any obstacles at the
inlet or the outlet of the indoor
unit
Remove the obstacles
Check the indoor fan speed Replace the fan motor
Excessively high air
temp. to the indoor unit
heat exchanger
Check whether or not the short-
circuited air exists
Remove the cause of the short-
circuited air
Excessively charged
refrigerant
Check the refrigerant quantity *4) Correctly charge the refrigerant
Non-condensate gas in
ref. cycle
Check the refrigerant quantity *4)
Recharge the refrigerant after the
vacuum pumping
Clogging of the
discharge pr. piping
Check for clogging Remove the clogging
Malfunction or internal leakage of the 4-way valve
Check the temp. difference at the
inlet and the outlet of the 4-way
valve
Replace the 4-way valve
Malfunction of the check valve of the outdoor unit
Check the temp. difference at the
inlet and the outlet of the check
valve
Replace the check valve
Excessively high suction
pressure
Malfunction or internal
leakage of 4-way valve
Check the temp. difference at the
inlet and the outlet of the 4-way
valve
Replace the 4-way valve
Discharge temp. of the indoor unit is unstable
Check the expansion valve of the
indoor unit in the same system
Replace the failed expansion
valve of the indoor unit
8 Troubleshooting
202
SMGB0060 rev. 1- 12/2010