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Thermistors
Open detection Short detection
Symbol Name
TH3
TH6
TH7
TH8
– 40:[-40˚F] or below
– 40:[-40˚F] or below
– 40:[-40˚F] or below
– 27:[-17˚F] or below
90:[194˚F] or above
90:[194˚F] or above
90:[194˚F] or above
102:[216˚F] or above
Thermistor <Outdoor pipe>
Thermistor <Outdoor 2-phase pipe>
Thermistor <Outdoor>
Thermistor <Heatsink>
Error Code
Abnormal point and detection method
Case
Judgment and action
U5
(4230)
Temperature of heatsink
Abnormal if heat sink thermistor(TH8)
detects temperature indicated below.
A12, 18, 42N··············84:, 183˚F
A24, 30, 36N··············81:, 177˚F
1 The outdoor fan motor is
locked.
2 Failure of outdoor fan motor
3 Air flow path is clogged.
4 Rise of ambient temperature
5 Defective thermistor
6 Defective input circuit of
outdoor power circuit board
7 Failure of outdoor fan drive
circuit
12 Check outdoor fan.
3 Check airflow path for cooling.
4 Check if there is something which causes
temperature rise around outdoor unit.
(Upper limit of ambient temperature is 46:
[114˚F].)
Turn off power, and on again to check if U5
is displayed within 30 minutes.
If U4 is displayed instead of U5, follow the
action to be taken for U4.
5 Check resistance value of thermistor (TH8)
or temperature by microcomputer.
(Thermistor/TH8: Refer to 10-6.)
(SW2 on A-Control Service Tool: Refer to 10-
10.)
6 Replace outdoor power circuit board.
7 Replace outdoor controller circuit board.
U3
(5104)
Open/short circuit of discharge
temperature thermistor (TH4)
Abnormal if open (3: [37˚F] or less) or
short (217: [422˚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 outdoor 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 10-9.
2 Check resistance value of thermistor (TH4) or
temperature by microcomputer.
(Thermistor/TH4: Refer to 10-6.)
(SW2 on A-Control Service Tool: Refer to 10-
10.)
3 Replace outdoor controller board.
U4
(TH3:5105)
(TH6:5107)
(TH7:5106)
(TH8:5110)
Open/short of outdoor unit thermistors
(TH3, TH6, TH7, and TH8)
Abnormal if open or short is detected
during compressor operation.
Open detection of thermistors TH3 and
TH6 is inoperative for 10 seconds to 10
minutes after compressor starting and 10
minutes after and during defrosting.
WCheck which unit has abnormality in its
thermistor by switching the mode of
SW2. (PAC-SK52ST)
(Refer to 10-10.)
1 Disconnection or contact failure
of connectors
Outdoor controller circuit
board: TH3,TH6/TH7
Outdoor power circuit board:
CN3
2 Defective thermistor
3 Defective outdoor controller
circuit board
1 Check connection of connector (TH3,TH6/TH7)
on the outdoor controller circuit board.
Check connection of connector (CN3) on the
outdoor power circuit board.
Check breaking of the lead wire for thermistor
(TH3,TH6,TH7,TH8). Refer to 10-9.
2 Check resistance value of thermistor
(TH3,TH6,TH7,TH8) or check temperature by
microcomputer.
(Thermistor / TH3, TH6, TH7, TH8 : Refer to 10-6.)
(SW2 on A-Control Service Tool: Refer to 10-
10.)
3 Replace outdoor controller circuit board.
WEmergency operation is available in case of
abnormalities of TH3, TH6 and TH7.
Refer to 10-8.
(
)
U6
(4250)
Power module
Check abnormality by driving power module
in case overcurrent is detected.
(UF or UP error condition)
1 Outdoor stop valve is closed.
2 Decrease of power supply voltage
3 Looseness, disconnection or
converse of compressor wiring
connection
4 Defective compressor
5 Defective outdoor power circuit
board
1 Open stop valve.
2 Check facility of power supply.
3 Correct the wiring (U·V·W phase) to
compressor. Refer to 10-9 (Outdoor power
circuit board).
4 Check compressor referring to 10-6.
5 Replace outdoor power circuit board.
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