BACnet/MSTP communication to Viconics VT thermostats is intermittent.

Issue

BACnet/MSTP communication to Viconics VT thermostats is intermittent.

Product Line

TAC I/A Series

Environment

  • BACnet
  • Viconics VT thermostats

Cause

Possible cause is physical layer and device addresses.

Resolution

Verify the physical layer (i.e. wire, end of line resistors and bias resisters) is installed as recommended.  A common wiring error is landing the trunk cable shield to the "REF" terminal at the thermostat. The shield should be carried through but not landed at the thermostat and the trunk shield should be grounded in one place.

Duplicate device addresses can cause this type of issue as well. Verify each controller has a unique "Com addr" which is part of its instance number. This can be viewed and modified from the display panel of the thermostat.

To enter the configuration parameter menu:

  • VT7200 series press and hold the button(OVERRIDE) for 8 seconds
  • VT7300 series press and hold the middle button(°C/F or OVERRIDE)for 8 seconds.
  • VT7600 series press and hold the button(MENU)for 8 seconds