UNT Controller—Unitary (UNT) Controller
65
An earth ground connection to the common terminal of the UNT110/111,
UNT120/121, and UNT140/141 series controllers is allowed for the
24 VAC power supply and the binary output/triacs (when set up for high
side switching). If this earth ground connection exists, it must be at the
transformer secondary common terminal only. There should be 0 VAC
measured from a common terminal to earth ground and over 20 VAC from
a 24 VAC terminal to earth ground, when power is applied. If no earth
ground connections were planned for the power supply and/or triacs, and
you suspect that an earth ground may exist, use the procedure described
above for the UNT100/101 controller to test for the presence of a ground
loop condition.
!
CAUTION: You may have a maximum of one single earth ground
connection, which must be at the transformer
secondary common, whether one or multiple
controllers are powered by the same transformer.
Table 26 indicates symptoms and corrections for possible controller
malfunctions. We recommend the use of HVAC PRO for Windows
Commissioning mode during all troubleshooting procedures.
Note: While in the commissioning program, you are actively viewing the
controller’s inputs and outputs. The screens will automatically
refresh the data values when the controller senses a change in
value.
Grounding
UNT110/111,
UNT120/121, and
UNT140/141 with
an Earth Ground
Connection
Troubleshooting
the UNT
Controller with
HVAC PRO for
Windows
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