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© 2012 Emerson Climate Technologies, Inc.
Printed in the U.S.A.
AE4-1395
Application Engineering
BULLETIN
Observe the compressor
suction &discharge
pressures
Are pressures
changing with the
modulation
cycle?
Operation
is normal
Yes
No
Yes
Yes
Measure the resistance
of the coil
Is the compressor
running?
Is the compressor
overheated?
Perform troubleshooting
to determine why the
compressor isn’t
running
Allow time to cool
Put the system back into
operation and retest
Start
Measure the voltage at
the modulation coil
terminals
Is voltage present,
coinciding with the
modulation cycle?
Troubleshoot the
modulation control
WARNING!
Disconnect and lockout
the power before
proceeding
Remove one wire from
the modulation coil
Coil has continuity
and isn’t grounded?
Replace modulation
coil
Replace modulation
valve,follow valve
replacement
instructions
Put the system back into
operation and retest
No
No
No
Yes
No
Yes
Figure 10
Modulation Troubleshooting