Carrier 38MGRBQ18B-3 - DIAGNOSIS AND SOLUTION (CONT); Low Pressure Protection Diagnosis

38MGRBQ: Service Manual
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
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DIAGNOSIS AND SOLUTION (CONT)
P2/PC 31 (Low pressure protection) diagnosis and solution
Troubleshooting
ERROR CODE
P2/PC 31
MALFUNCTION DECISION
CONDITIONS
If the sampling voltage is not 5V, the LED will display the failure.
SUPPOSED CAUSES
Wiring mistake
Faulty overload protector
System block
Faulty Outdoor PCB
L
o
w
Low pressure protection
Is the wiring between
between the low pressure
protector and main control
board is connected well?
Met
h
o
d
: Disconnect t
h
e p
l
u
g
.
Me
a
s
u
re the resist
a
nce
of
the
low
p
ressure
p
rotector
.
If th
e
Method: Disconnect the plug.
Measure the resistance of the
low pressure protector. If the
protector is normal the value is 0.
Yes
Yes
Tighten the connection
Replace outdoor main board
No
Replace the low pressure protector
No
Is the low pressure
protector broken?
C
heck whether the outdoo
r
l
ow
Check whether the outdoor
ambient temperature is too
low
No
Stop the unit Yes
No
of high
p
Check whether valve core
of high pressure valve is
opened
Refer to the Fan Speed Out of
Control solution. Determine the
cause and solve it.
No
Yes
Yes
No
Check whether the refrigerant
system is ok
No
Fully open the high
pressure valve’s valve core
Check if the indoor fan runs
properly in the COOLING mode.
Refrigerant is low. Add more.