Bosch BMS500-AAU036-1AHCXC - Low Pressure Protection (PC 31)

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Service Manual
Bosch Climate 5000 Series Ductless Air Conditioner / Heat Pump Multi Zone Outdoor Units (01.2023)
8.6.9 Low pressure protection (PC 31)
Error Code PC 31
Malfunction decision conditions If the sampling voltage is not 5V, the LED will display the failure.
Supposed causes
f Improper / Incorrect Wiring
f Over load protector faulty
f System blockage
f Outdoor PCB faulty
Table 40
Troubleshooting:
Figure 73
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Low pressure protection
Check whether the wiring
between the low pressure
protector and the outdoor
PCB is correct and well
connected
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Method:Disconnectthe plug.
Measurethe resistance of the
lowpressure protector. If the
protectorisnormalthe value
should be o
Yes
Yes
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Replaceoutdoor PCB
No
No
Check if low pressure
protector is damaged
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Checkwhether theoutdoor
ambienttemperature
is too low
No
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Stop thesystemYes
No
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Check whethervalve core
of high pressure valveis
opened
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Checkifthe indoor fanruns
properly in coolingmode
No
Yes
Yes
No
System should operate normally
Yes
Correct wiring
Replace the low pressure protector
Fully open valve core of
high pressure valve
Please refer to the solution of fan
speed has been out of control
malfunction. Find out the cause and
have it solved
Does the system has sufficient
amount of refrigerant?
No
Charge the unit with proper
amount of refrigerant as
defined in the IOM