507746-01
Issue 1821
Page 18 of 39
Table 10.
Air Handler Control Connections
Indoor Control
Terminal Label
Function
Non-Communicating Room Thermostat
(Indoor and Outdoor -24 volts)
Indoor Communicating Outdoor Non-
Communicating
Full Communication
(Indoor & Outdoor)
W1 (Input)
Indicates a first-stage heating demand. This
input is an anticipator for the thermostat.
N/A
N/A
W2 (Input)
Indicates a second-stage h eating demand.
W1 input must be active to recognize
second-stage heat demand.
N/A
N/A
W3 (Input)
Indicates a third-stage heating demand. W1
and W2 inputs must be active to recognize
third-stage heat demand.
N/A
N/A
Y1 & Y2 (Input/
Output)
Room thermostat inputs 24 volts to the Y1
and Y2 terminals on the indoor control.
The 24 volt signal is then passed through
to the outdoor unit. During a second-stage
demand, both Y1 and Y2 are active. The Y1
terminal is connected to Y2 by link (Solid
jumper on control that would be cut for 2
stage applications).
The room thermostat communicated
with the indoor control. The indoor
control outputs 24 volts on i ts Y1 and
Y2 terminals which are hard wired to the
non-communicating outdoor unit.
In a full communicating
system, no wiring is
required on Y1 and Y2
terminals.
G (Input)
Indicates a 24 volt indoor blower demand.
In a communicating system, ”G” input to indoor control is used by
non-communicating IAQ devices (such as LVCS, HRV or ERV) to
ensure indoor blower demand.
C
The C terminal shall interconnect the signal ground of the room thermostat with secondary transformer ground (TR)
and chassis ground (GND).
R
The R terminal shall be capable of providing the power to the thermostat and all the associated loads.
O (Input/
Output)
Room thermostat inputs 24 volts to the
O terminal on the indoor control. The O
terminal is connected to R by link (Solid
jumper on control that would be cut if unit
was a heat pump).
The room thermostat communicated with
the indoor control. The indoor control
outputs 24 volts on its O terminals which
are hard wired to the non-communicating
outdoor unit. If there is 24 volts on O, the
reversing valve will be energized and the
outdoor unit will run in the cooling mode.
If O does not have 24 volts, the outdoor
unit will run in heating mode.
In a full communicating
system, O terminal is
not wired.
DS (Input)
Used for Harmony III zoning systems, or
thermostat with dehumidification capability.
The DS terminal is connected to R by link
(Solid jumper on control that would be cut if
for the above applications).
Harmony III control - This will allow the
control to vary the voltage signal to the
indoor b lower motor to control required
CFM.
Dehumidification - Allow a 24 volt
signal on the DS to turn off and on the
dehumidification mode.
N/A
N/A
DH (Output)
The DH terminal provides a 24VAC output for dehumidification needs in communicating systems.
H (Output)
The H terminal provides a 24VAC output for humidification needs in both communicating and non-communicating
mode.