Troubleshooting; Troubleshooting Tips; Exterior Fault Troubleshooting - Danfoss VLT HVAC Drive FC 100 Service Manual

High Power Service Manual for VLT
Adjustable Frequency Drives

4 Troubleshooting

4.1 Troubleshooting Tips

Before attempting to repair an adjustable frequency drive, here are some tips to follow to make
the job easier and possibly prevent unnecessary damage to functional components.
1. Note all warnings concerning voltages present in the adjustable frequency drive. Always
verify the presence of AC input voltage and DC bus voltage before working on the unit.
Some points in the adjustable frequency drive are referenced to the negative DC bus and
are at bus potential even though it may appear on diagrams to be a neutral reference.
Remember that voltage may be present for as long as 40 minutes on E-frame
size adjustable frequency drives or 20 minutes on D-frame size adjustable
frequency drives after removing power from the unit. See the label on the
front of the adjustable frequency drive door for the specific discharge time.
2. Never apply power to a unit that is suspected of being faulty. Many faulty components
within the adjustable frequency drive can cause damage to other components when
power is applied. Always perform the procedure for testing the unit after repair as de-
scribed in Section 5, Test Procedures.
3. Never attempt to defeat any fault protection circuitry within the adjustable frequency
drive. That will result in unnecessary component damage and may cause personal injury.
4. Always use factory approved replacement parts. The adjustable frequency drive has been
designed to operate within certain specifications. Incorrect parts may affect tolerances
and result in further damage to the unit.
5. Read the instruction and service manuals. A thorough understanding of the unit is the
best approach. If ever in doubt, consult the factory or authorized repair center for as-
sistance.

4.2 Exterior Fault Troubleshooting

There may be slight differences in servicing an adjustable frequency drive that has been opera-
tional for some extended period of time compared to a new installation. When using proper
troubleshooting procedures, make no assumptions. To assume a motor is wired properly because
the adjustable frequency drive has been in service for some time may cause you to overlook loose
connections, improper programming, or added equipment, for example. It is best to develop a
detailed approach, beginning with a physical inspection of the system. See Table 4-1, Visual In-
spection, for items to examine.
®
FC Series
MG.90.L1.22 - VLT ® is a registered Danfoss trademark
4 Troubleshooting
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