Carrier 25VNA Service Manual page 21

Start
Verify scroll temp
fault condition at
the system
controller
Is the system
A
operable ?
Yes
No
WARNING!
Disconnect &
lock - out power,
allow 2 minutes
for drive to
discharge
Disconnect 4-pin
plug from drive
(See Fig. 18)
Measure
resistance
between unit
ground and
black, white, &
red wires in the
plug
Is there continuity
B
to ground ?
Yes
No
A good
reading is
equal to
infinite Ω
Measure
resistance
between black &
white wires in the
4-pin plug
Resistance
is in the
Is resistance
range that
265Ω to 337KΩ?
Yes
will allow
operation
No
Refer to
thermistor
Is compressor
resistance -
No
hot ?
temperature data
(See Fig. 14)
Yes
Allow time for
compressor to
Is resistance
cool & resistance
0Ω?
to change (60
minutes )
Measure
Allow time for
resistance
resistance to
between black &
change (60
white wires in the
minutes )
4-pin plug
Is resistance
A
265 Ω- 337KΩ ?
Yes
No
Refer to
thermistor
Is Ω moving towards
resistance -
Ω corresponding to
temperature data
ambient temp ?
(Figure 14)
Fig. 12 – Scroll Temp Troubleshooting - - Part 1
A
Yes
No
Power down the
entire system for
2 minutes to
reboot the drive
No
Yes
If problem still
exists, change
the compressor
21
Thermistor
circuit is
shorted
WARNING!
Recover system
refrigerant
charge
Remove the
molded plug from
the thermistor
fusite on the
compressor
(See Fig. 19)
Measure
resistance in
scroll thermistor
circuit pins
Figure
(See Fig. 20)
Scroll thermistor
circuit is shorted
Is resistance
internally - replace
Yes
0Ω?
compressor
No
Inspect molded
plug assembly
for lead to lead
shorting
Install new
molded plug
assembly and
carefully route
wires
A
A12036