Actual Flow Water Temperature Thermistor (Th1); Pipe Temperature Thermistor/Liquid; Freezing/Overheating Protection Is Working; Actual Tank Temperature Thermistor - Mitsubishi Electric PUHZ-SHW230YKA2 Service Manual

Check Code
Abnormal point and detection method
Actual flow water temperature thermis-
tor (TH1)
1 The unit is in 3-minute resume
prevention mode if short/open of
thermistor is detected. Abnormal if the
unit does not reset normally after 3
minutes. (The unit returns to normal
operation, if it has been reset normally.)
2 Constantly detected during cooling,
P1
heating ECO, anti freeze, hot water and
heating operation.
Short: −90: or more
Open: −40: or less

Pipe temperature thermistor/Liquid

(TH2)
1 The unit is in 3-minute resume
prevention mode if short/open of
thermistor is detected. Abnormal if the
unit does not reset normally after 3
minutes. (The unit returns to normal
operation, if it has been reset normally.)
2 Constantly detected during cooling,
P2
heating ECO, anti freeze, hot water and
heating (except defrosting) operation
Short: 90: or more
Open: −40: or less

Freezing/overheating protection is working

1 Freezing protection (Cooling mode)
The unit is in 6-minute resume preven-
tion mode if pipe temperature stays
under −15: for 3 minutes, 3 minutes
after the compressor started. Abnormal if
it stays under −15: for 3 minutes again
within 16 minutes after 6-minute resume
prevention mode.
P6
2 Overheating protection (Heating, heating
ECO, Anti freeze, Hot water mode)
The units is in 6-minute resume preven-
tion mode if pipe temperature is detected
as over 70: after the compressor start-
ed. Abnormal if the temperature of over
70: is detected again within 30 minutes
after 6-minute resume prevention mode.
Actual tank temperature thermistor (TH5/
THW5)
1 The unit is 3-minute resume preven-
tion mode if short/open of thermistor is
detected. Abnormal if the unit does not
reset normally after 3 minutes. (The unit
returns to normal operation, if it has been
reset normally)
2 Constantly detected during cooling,
P9
heating, heating ECO, anti freeze and
hot water operation.
OCH594B
Cause
1 Defective thermistor
characteristics
2 Breaking of wire or contact
failure of thermistor wiring
3 Defective PCB of Interface unit/
Flow temp. controller
Refer to the indoor unit's Installation
Manual for TH1 connection.
1 Defective thermistor
characteristics
2 Breaking of wire or contact
failure of thermistor wiring
3 Defective refrigerant circuit is
causing thermistor temperature
of 90: or more or −40: or
less.
4 Defective PCB of Interface unit/
Flow temp. controller
Refer to the indoor unit's Installation
Manual for TH2 connection.
(Cooling mode)
1 Short cycle of air path
2 Low-load (low temperature) op-
eration out of the tolerance range
3 Defective outdoor fan control
4 Overcharge of refrigerant
5 Defective refrigerant circuit
(clogs)
(Heating mode)
1 Short cycle of air path
2 Overload (high temperature) op-
eration out of the tolerance range
3 Defective outdoor fan control
4 Overcharge of refrigerant
5 Defective refrigerant circuit (clogs)
6 Bypass circuit of outdoor unit is
defective.
1 Defective thermistor character-
istics
2 Breaking of wire or contact
failure of thermistor wiring
3 Defective PCB of interface unit/
Flow temp. controller
Refer to the indoor unit's
Installation Manual for TH5/THW5
connection.
25
Judgment and action
1–2 Check resistance value of thermistor.
0: 15.0 k"
10: 9.6 k"
20: 6.3 k"
30: 4.3 k"
40: 3.0 k"
If you put force on (draw or bend) the lead wire
with measuring resistance value of thermistor,
breaking of wire or contact failure can be detected.
3 Check actual flow water temperature display
on remote controller.
Replace PCB of Interface unit/Flow temp.
controller if there is abnormal difference with
actual flow water temperature.
Turn the power off, and on again to operate
after check.
1–2 Check resistance value of thermistor.
For characteristics, refer to (P1) above.
3 Check pipe <liquid> temperature with remote
controller in test run mode. If pipe <liquid>
temperature is extremely low (in cooling
mode) or high (in heating mode), refrigerant
circuit may have defective.
4 Check pipe <liquid> temperature with remote
controller in test run mode. If there is ex-
tremely difference with actual pipe <liquid>
temperature, replace PCB of Interface unit/
Flow temp. controller.
Turn the power off, and on again to operate
after check.
(Cooling mode)
1 Remove blockage.
3 Check outdoor fan motor.
45 Check operating condition of refrigerant
circuit.
(Heating mode)
1 Remove blockage.
3 Check outdoor fan motor.
4–6 Check operating condition of refrigerant
circuit.
1–2 Check resistance value of thermistor.
0: 15.0 k"
10: 9.6 k"
20: 6.3 k"
30: 4.3 k"
40: 3.0 k"
If you put force on (draw or bend) the lead wire
with measuring resistance value of thermistor,
breaking of wire or contact failure can be detected.
3 Check actual tank temperature display on
remote controller.
Replace PCB of Interface unit/Flow temp.
controller if there is abnormal difference with
actual tank temperature.
Turn the power off, and on again to operate
after check.