Manual & Installer Guide 74
Before you go any further, determine your existing
wiring and equipment situation.
A. If you have a Heating only system without Air Conditioning, the ProStat+
thermostat will require 3 wires: R (24Vac), C (24Vac) and W (Heat). Most systems
that only have Heating use very simple thermostats that require 2 wires: the
R (24Vac) and W (Heat). The ProStat+ thermostat requires 3 wires to the
thermostat. In this case an Add-a-Wire accessory will not work and it will be
necessary to install another wire for the C (24Vac) connection.
B. If you have a single stage fossil fuel heater with air conditioning, the ProStat+
model will require 5 wires for independent fan control. They are R (24Vac), C
(24Vac), W (Heat), Y (Cooling), and G (Fan). You may connect only 4 wires, as
instructed in the “Making 4 Wires Work When 5 Wires Are Required” section on
page 76.
If there are only 4 wires present that are connected to the existing thermostat, there
are at least 3 options available to connect the ProStat+ thermostat:
1. Use the 4 wires as instructed in the“Making 4 Wires Work
When 5 Wires Are Required” section on page 76, and note that
the fan will only operate with a Heating or Cooling demand.
2. Pull new thermostat wire from the HVAC equipment to the
thermostat so that there are at least 5 wires available.
3. Purchase and install a ProStat+ Add-A-Wire accessory.
C. If you have a multi-stage HVAC system comprised of a fossil fuel heater with
air conditioning, the ProStat+ thermostat will require the 5 wires mentioned
above (R, C, W, Y, G) plus an additional wire for each additional stage of Heating
or Cooling. You may reduce the 5 wire requirement to 4 if you give up independent
fan control following the instruction in the “Making 4 Wires Work When 5 Wires Are
Required” section on page 76, or use the optional Add-A-Wire accessory.
Installation Instructions – Wire Connections
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