Mitsubishi Electric PUZ-A18NHA2 Service Manual page 38

Abnormal point and detection method
Error Code
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
U3
compressor starting process and for 10
(5104)
minutes after and during defrosting.)
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)
U4
(Refer to 10-10.)
(TH3:5105)
(TH6:5107)
(TH7:5106)
(TH8:5110)
Symbol
TH3
TH6
TH7
TH8
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
U5
(4230)
Power module
Check abnormality by driving power module
in case overcurrent is detected.
(UF or UP error condition)
U6
(4250)
1 Disconnection or contact
failure of connector (TH4) on
the outdoor controller circuit
board
2 Defective thermistor
3 Defective outdoor controller
circuit board
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
Thermistors
Name
Thermistor <Outdoor pipe>
Thermistor <Outdoor 2-phase pipe>
Thermistor <Outdoor>
Thermistor <Heatsink>
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
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
Case
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.
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.
Open detection
– 40:[-40˚F] or below
– 40:[-40˚F] or below
– 40:[-40˚F] or below
– 27:[-17˚F] or below
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.
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.
38
Judgment and action
Short detection
90:[194˚F] or above
90:[194˚F] or above
90:[194˚F] or above
102:[216˚F] or above