Thermostat / Low Voltage Connections; Twinning; One Stage Heating - Oxbox J951X U Series Installation Instructions Manual

Field Line Voltage Wiring
Factory Line Voltage Wiring
Green or Bare (Ground)
Junction Box (may be int. or ext. to the furnace). These connections can be made in the field supplied disconnect at the furnace.
NOTE: Connections made within the furnace burner compartment do not require a junction box.

Thermostat / Low Voltage Connections

• The furnace is designed to be controlled by a 24 VAC
thermostat. The thermostat's wiring must comply with the
current provisions of the NEC (ANSI/NFPA 70) and with
applicable local codes having jurisdiction.
• The thermostat must be installed according to the
instructions supplied by the thermostat manufacturer.
Low voltage connections (24 VAC) from the thermostat
are wired to the terminal strip on the integrated control
in the furnace.
Figure 26
for heating only (two-wire) and heating/cooling (four-wire)
applications. Recommended minimum wire gauge for
thermostat wiring is shown in
• The thermostat should be mounted about 5 feet above
the floor on an inside wall. DO NOT install the thermostat
on an outside wall or any other location where its
operation may be adversely affected by radiant heat from
fireplaces, sunlight, or lighting fixtures, and convective
heat from warm air registers or electrical appliances.
Refer to the thermostat manufacturer's instruction sheet
for detailed mounting information.

Twinning

WARNING:
When servicing either twinned furnace, power
must be turned off on both furnaces. Failure to
comply may result in improper operation leading
to damage to the furnaces or personal injury!
Single stage furnaces are not supplied with a built-in twinning
capability. Other valuable features and enhancements were
made to the new control that made it necessary to remove
the twinning capability. For twinning of single stage furnaces
with PSC motors, a twinning kit is available for purchase.
Refer to the technical sales literature for part numbers. Please
follow the instructions provided with the kit.
Single stage furnaces are equipped with a fixed speed blower;
therefore, the twin terminal on the blower control boards
( ) may be used to twin the single stage
Figure 27 (page 25)
furnaces. The twinning system requires a relay (P/N 624843)
in the secondary furnace for proper twinning.
For proper twinning of fixed speed furnaces the following
criteria must be met:
• Both furnaces and motors must be the same size.
• Both motors must be on the same speed for cooling and
heating.
24
Field Supplied
Fused Service
Panel
Black (Hot)
White (Neutral)
Ground
Figure 25. Line Voltage Field Wiring
contains the proper connections
.
Table 5 (page 23)
Field Supplied
Disconnect within
Field Supplied
Sight of Furnace Panel Connector
Black
Black
White
White
Ground
A/C
CONDENSING
UNIT
3 AMP
ROOM
FUSE
THERMOSTAT
R
Connect
C
R & W
Y
For Heating
G
Only
W
9 6 3
2
NOTE: The "Y" terminal 8 5
on the control board must 4 1
7
be connected to the
thermostat for proper
6 3
cooling mode operation.
2
5
4 1
FIELD WIRING
LOW VOLTAGE
CONNECTION
NEUTRAL LEADS
HUMIDIFIER TAP
Figure 26. Low Voltage Field, Four-wire
Heating/Cooling Applications
• Both furnaces must have a common return duct and
common supply plenum.
• Both furnaces must be the same phase and on the same
leg of power.
• Furnaces equipped with variable speed iSEER™
motors may not be twinned under any circumstances.
For twinning of single stage furnaces equipped with
fixed speed blowers, refer to
instructions:
1. Turn off all power to both furnaces.
2. Attach a wire between the two twin terminals on the blower
control boards. Use field supplied wire and 3/16" wire
terminals.
NOTE: One furnace can be used for one stage of heating
and the other furnace can be used for the second stage of
heating. The installer also has the choice of running one
furnace only or both furnaces. In both cases the blowers will
run at the same time and at the same speeds:

One stage heating

• Connect the thermostat wires to the primary furnace
control board. Mount the relay on the bracket on the
secondary furnace.
• Connect W from the primary furnace to the coil side of the
relay (using field supplied wire and 3/16" terminals).
Black
White
Ground
JUMPER PIN
SETUP
CONDENSING UNIT
CONTROL BOX
H
MH
ML
L
SPEED
SELECT
STATUS
RED
GREEN
FLAME
YELLOW
180
BLOWER
120
OFF
90
DELAY
60
180
120
90
60
MOTOR
SPEED
TAPS
ELECTRONIC AIR CLEANER
and the following
Figure 27