73 Manual & Installer Guide
Before you go any further, determine what your
existing wiring and equipment situation is.
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 75.
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 75, 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 instructions in the “Making
4 Wires Work When 5 Wires Are Required” section on page 75, or use the
optional Add-A-Wire accessory.
Installation Instructions – Wire Connections
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