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U2
(1102)
(1) High discharging temperature
Abnormal if discharge temperature ther-
mistor (TH4) exceeds 125: [257°F]
or
110: [230°F] continuously for 5 minutes.
Abnormal if pressure detected by high
pressure sensor and converted to satura-
tion temperature exceeds 40: [104°F]
during defrosting and discharge tem-
perature thermistor (TH4) exceeds
110: [230°F].
(2) Refrigerant shortage abnormality
1 When the conditions of below detecting
mode 1 or 2 are satisfied (1st detec-
tion) during the compressor operation,
the compressor stops and restarts
operation in 3 minutes.
<Detecting mode 1>
When the below conditions are satisfied
completely.
1. Compressor is operating in HEAT
mode.
2. Discharge superheat is 70
:
[158°F]
or more.
3. Difference of outer temperature
thermistor (TH7) and outdoor piping
temp. thermistor (TH3) applies to the
formula of (TH7-TH3)<5 degC
[9 degF].
4. High-pressure pressure sensor is
below about 2.04MPa [296PSIG].
<Detecting mode 2>
When the below conditions are satisfied
completely.
1. Compressor is operating.
2. When cooling, discharge superheat
is 80
:
[144°F] or more.
When heating, discharge superheat
is 90
:
[162°F] or more.
High pressure sensor is below about
2.32MPa [337PSIG].
2 When the conditions of detecting mode
1and 2 are satisfied again (2nd detec-
tion) within 30 minutes since the com-
pressor has stopped, it stops abnor-
mally. In this time, <U2> is displayed.
3 When the conditions of detecting
mode1and 2are satisfied again after
30 minutes since the compressor has
stopped (1st time), it becomes the 1st
detection and same performance as
above 1.
4 It is being delay for abnormal stop dur-
ing 30 minutes since the compressor
has stopped. In this time, check delay
code <U2> will be displayed.
1 Overheated compressor opera-
tion caused by shortage of
refrigerant
2 Defective operation of stop
valve
3 Defective thermistor
4 Defective outdoor controller
board
5 Defective action of linear
expansion valve
1 Gas leakage, Gas shortage
2 When heating operation, scant
refrigerant operation
(When heating, airflow or ther-
mo OFF are mixed-operation,
it causes a refrigerant shortage
operation.)
3 Ball valve performance failure
(Not fully opened.)
4 Error detection of discharge
super heat
1) High-pressure sensor defec-
tive
2) Discharge temperature ther-
mistor defective
3) Thermistor input circuit
defective and high-pressure
sensor defective in outdoor
controller board
5 Error detection of TH7/TH3
1) Thermistor defective
2) Thermistor input circuit
defective in outdoor control-
ler board
1 Check intake superheat.
Check leakage of refrigerant.
Charge additional refrigerant.
2 Check if stop valve is fully open.
34 Turn the power off and check if U3 is dis-
played when the power is turned on again.
When U3 is displayed, refer to “Judgement
and action” for U3.
5 Check linear expansion valve.
Refer to 8-6.
1 Check the refrigerant amount.
2 Check the operation condition and refrigerant
amount.
3 Check the ball valve is fully opened.
4 1) Check the ball valve is fully opened.
2) Check the resistance of discharge tem-
perature thermistor.
3) According to “Monitoring function for out-
door unit”, set the SW2 and check the
high-pressure sensor level.
According to “Monitoring function for outdoor
unit”, set the SW2 and check the discharge
temp. thermistor level.
When the high-pressure sensor and dis-
charge temp. thermistor are normal, if the
above mentioned detecting pressure level
and temp. are big different from the actual
pressure and temp., replace the outdoor con-
troller board.
5 1) Check the resistance of thermistor.
2) According to “Monitoring function for out-
door unit”, set the SW2 and check the out-
door pipe temp. thermistor level.
3) According to “Monitoring function for out-
door unit”, set the SW2 and check the
outer temp. thermistor level.
Error Code
Abnormal point and detection method
Judgment and action
Case
U3
(5104)
Open/short circuit of discharge
temperature thermistor (TH4)
Abnormal if open (3: [37°F] or less) or
short (217: [423°F] or more) is detected
during compressor operation.
(Detection is inoperative for 10 minutes
of compressor starting process and for 10
minutes after and during defrosting.)
1 Disconnection or contact failure
of connector (TH4) on the out-
door controller circuit board
2 Defective thermistor
3 Defective outdoor controller
circuit board
1 Check connection of connector (TH4) on the
outdoor controller circuit board.
Check breaking of the lead wire for thermistor
(TH4). Refer to 8-6.
2 Check resistance value of thermistor (TH4)or
temperature by microprocessor.
(Thermistor/TH4: Refer to 8-6.)
(SW2 on A-Control Service Tool:
Refer to 8-8.)
3 Replace outdoor controller board.