DCN: 141-00940-09 11/02/07
18
TXB16 Power Connection
Power from the HVAC System
The TXB16 Control Unit connects to the HVAC system’s thermostat connections and receives 24VAC
power from it.
All most all HVAC systems have standard thermostat connections. This may be a thermostat terminal strip
on the system control board or color coded wires. Typically, these connections are marked as follows:
Terminal Marking
Wire Color
Use
C
Blue
24VAC Common power
R
Red
24VAC Return power
G
Green
Fan signal
W
White
Heat signal
Y
Yellow
Cool signal (Compressor)
There may be others like orange, brown and black for other functions, refer to the HVAC wiring diagrams.
You must connect both 24VAC power connections to the TXB16 control unit:
the 24VAC common,
marked as C on the thermostat connections or the BLUE wire,
and
the 24VAC return
, marked R on the thermostat connection or the RED wire.
Note: If the HVAC system power is off, then power to the thermostat will be off as well.
HVAC System Transformer Types
Most Common Type:
By far the most common HVAC system is the Standard Gas central heating/cooling
forced air system with a single 24VAC power transformer. (Electric heating also falls into this category)
Separate Heating and Cooling systems:
These are essentially two systems with a common air handler
or blower. In this case there is a separate heating 24VAC transformer and a cooling 24VAC transformer.
This type of a system requires that the Control Unit be connected using a separate heating system power
input R terminal (RH) and a separate cooling system power input R terminal (RC). When connecting to
these systems you must “split” the RH/RC power connections on the HVAC control unit HVAC terminal
connections (J4). See wiring diagram for instructions on cutting this jumper, JP1.
Heat Pump Systems:
These systems have a common transformer like standard central heat/cool
systems. Wire the HVAC system R to either of the Control Unit’s RH or RC terminals.
Connecting the HVAC system power to the HVAC Control Unit
For all systems:
Connect the HVAC system 24VAC Common C (or Blue wire) to J4 24Com connection.
For Standard and Heat Pump systems:
Connect the HVAC system 24VAC Return R (red wire) to either the control units J4 RH or RC terminals
(they are jumpered together by JP1)
For “split” or separate heating /cooling transformers systems:
First CUT the jumper wire at JP1 (this separates the RH and RC terminals)
Connect the heating system’s R terminal (or red wire) to the control units J4 RH terminal.
Connect the cooling system’s R terminal (or red wire) to the control units J4 RC terminal.
