Venstar T2700 stuck in OFF mode when wired to Xenta controller

Issue

The thermostat appears to be in OFF mode and can't be cycled through the modes as indicated by the manufacturer's directions.
 

Product Line

TAC I/NET, TAC Vista, Andover Continuum, TAC I/A Series, Field Devices, SmartStruxure Solution

Environment

Venstar T2700, VST2700 thermostats for red-wire control connected physically to a controller

Cause

It seems that the polarity of the dry contact was set to the default Normally Open (NO) state. Using the Venstar EZ-Programmer to apply the correct settings for use with an occupancy point did not overwrite the polarity of the Venstar's dry contact, but did overwrite the Dry Contact Operation. Also, by wiring everything up first, we did not power up the thermostat to change the mode before it got the closed dry contact command from the BAS. So when we did power everything up, the dry contact was closed, but the thermostat understood that this was an "unoccupied" command since it was still set to NO.

Even though the security settings allowed the mode to be changed, when Dry Contact Operation is enabled, the mode can only be changed in occupied mode. When the thermostat goes unoccupied, it stays
in whatever mode it was in previously, and controls to the unoccupied setpoints. By not realizing that the EZ Programmer didn't overwrite the polarity, we assumed the dry contact operation and polarity were correct
and a closed dry contact would enable the occupied mode.



 

Resolution

This issue can be resolved by powering up the thermostat before connecting the dry contact relay and changing the mode to "auto". If already wired, make sure the dry contact polarity is set to Normally
Closed (NC) and Dry Contact Operation is "Yes". Then the modes can be cycled while occupied.