Support Module Installation and Wiring
37
ViewStat Communicating Thermostat
Applications

Heat Pump Applications

If the support module is being used with a heat pump thermostat with auxiliary heat, the thermostat can be
configured to disable the use of auxiliary heat during warm weather and to lock out the compressor when the
outdoor temperature is too cold. This allows for the most efficient use of energy.
At warmer temperatures, a heat pump will operate much more efficiently than the auxiliary heat. It can save
energy to disable auxiliary heat in some cases, for example, when returning from a setback on a mild day. The
temperature above which auxiliary heat is disabled is the auxiliary lockout temperature or high balance point.
Refer to the thermostat user manual for a detailed explanation.
Air-to-air heat pumps become less efficient as the outdoor temperature drops. The temperature at which it
becomes more efficient to use auxiliary heat instead of the heat pump is the balance point or l ow balance point.
Configure the temperature sensor (T1/T2) that you are using to sense outdoor temperature to the "Monitor"
mode by setting the DIP switch 3 to the "off" position and the support module address to number 1. The high
and low balance points are set at the thermostat.

Humidity Control (VST-TRH only)

In order to set your thermostat up as a humidity controller, you will need at least one (up to four for averaging)
VST-TRH (temperature/humidity) support module(s) wired to the thermostat.
1. Locate the VST-TRH Support Module in the area that you want to control humidity.
2. Set the T3/T4 sensor (Humidity) Input to "Control" by moving the # 4 DIP switch to the "on" position.
Up to four T3/ T4 humidity sensors can be set to control and the reported values will be averaged and
displayed on the thermostat.
3. Once the humidity control sensor(s) have been wired to the ViewStat, the thermostat display will change
to indicate % RH instead of °F/°C. The thermostat mode selections will also change to reflect humidity
control. The modes are "Humidify", "Dehumidify", "Humidify or Dehumidify" and "Off". Humidification/
Dehumidification set points are changed the same way that temperature control set points would be
changed.
Mode of Operation Set to "Humidify"
The B terminal is continually energized in the "Humidify" mode. When the thermostat calls for humidity, the
W1/HUM terminal will energize. If the minimum off time of 2 minutes has not elapsed since the previous call,
no terminals will energize until it has. All energized terminals will remain energized for the minimum on time
of 2 minutes.
Mode of Operation Set to "Dehumidify"
The O terminal is continually energized in the "Dehumidify" mode. When the thermostat calls for
dehumidification, the Y1/DEHUM terminal will energize. If the minimum off time of 4 minutes has not
elapsed since the previous call, no terminals will energize until it has. All energized terminals will remain
energized for the minimum on time of 4 minutes.
The ViewStat will not display temperature or humidity (Sensor 1 or Sensor 2) values if
DIP switch 6 is set to T1/T2 without wiring a sensor to the T1/T2 terminal.
If a sensor is connected to the T1/T2 terminal; DIP switch 6 MUST be set to Off or an
invalid temperatures will be reported to the ViewStat.
None of the temperature sensors connected to this ViewStat can be set to control
mode because a control temperature input to the ViewStat will override a control
humidity input. Make sure all temperature sensors connected to this ViewStat are set
to "Monitor".