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Control unit installation
Install the control unit in a protected, convenient, indoor location near the HVAC system or in a service
accessible area such as an equipment closet or garage. Mount the control unit in a vertical position on a wall or
sturdy structural member. If you mount the control unit on the HVAC system, be careful to avoid the hot burner
section and high vibration areas.
The control unit is connected to the HVAC system and to the WDU unit as well as the serial communication
and power connections.
Control unit to WDU wiring
Connect the WDU to the control unit with existing thermostat wiring in retrofit installations. For new
installations, 22/24 Ga twisted-pair, typically CAT 3 or CAT 5 wiring is preferred (Figure 17).
Figure 17. Control unit to WDU wiring
Control unit to HVAC wiring
Electrically, the control unit looks like a standard thermostat to your HVAC system. All connections to the
HVAC system are made at the normal thermostat connections on the HVAC unit. Refer to your HVAC system’s
documentation for specific information on its thermostat connections and set up requirements. You will need to
know the following:
HVAC system type. Gas, electric, heat pump, radiant, or hydronic.
Fan requirement. No fan with heat or fan with heat.
For heat pump system. Changeover with cool or with heat (O or B connection).
Retrofit wiring
You may find that you have additional wires when you disconnect your old thermostat. Usually these wires are
for auxiliary functions such as filter or trouble indicators. For heat pump systems there may be emergency heat
(EH) wiring or both O and B changeover connections. These wires are not used in the SmartCommand
installation and, in most cases, these extra wires are not required for normal HVAC system operation. See
HVAC wiring for wiring diagrams for your type of HVAC system: standard or heat pump.
CAUTION: Do not miswire the power and data lines, damage will result. Check your wiring before applying power.
Wall display unit
Control unit
J1
GND
+12V
Clock
Data
GND
+12 VDC
Clock
Data