035-17438-001 Rev. A (901)
Unitary Products Group
13
24 Volt Connections
This variable airflow furnace includes a CFM selection board
in the lower part of the electrical control box. All field wiring
connections should be made to this terminal block.
Connection diagrams are shown above in Figures 9 and 10.
Select the correct diagram for your particular heating and
cooling system.
SAFETY CONTROLS
Blower Door Safety Switch
This unit is equipped with an electrical interlock switch
mounted in the blower compartment. This switch interrupts all
power at the unit when the panel covering the blower com-
partment is removed.
Electrical supply to the unit is dependent upon the panel that
covers the blower compartment being in place and properly
positioned.
Rollout Switch Controls
These controls are mounted on the burner assembly. If the
temperature in the burner compartment exceeds its set point,
the ignitor control and the gas valve are deenergized. This is
a manual reset control and must be reset before operation
can continue.
The operation of this control indicates a malfunction in the
combustion air blower or a blocked vent pipe connection.
Pressure Switch
This furnace is supplied with two differential pressure
switches which monitor the flow through the furnace and
venting system. This switch de-energizes the ignition control
module and the gas valve if any of the following conditions
are present:
1.
Blockage of internal flue gas passage ways.
2.
Blockage of vent piping.
3.
Failure of combustion air blower/motor.
Limit Control
The high temperature limit control is located on the furnace
vestibule panel just to the right and above the gas valve. This
is an automatic reset control and provides over temperature
protection due to reduced airflow, such as a dirty filter or
blower motor failure.
Auxiliary Limit Controls
These high temperature limit controls are located in the
blower compartment, one on each side on upflow/horizontal
unit. Downflow units have a single limit mounted on the
blower assembly. These are manual reset controls and give
high temperature protection when the unit is applied in the
horizontal position.
Control Circuit Fuse
A 3 amp fuse is provided to protect the 24 volt transformer
from overload caused by control circuit wiring errors. This is
an ATO 3, automotive type fuse and is located in the unit wir-
ing harness between the control transformer and the furnace
control.
FIGURE 10 :
Field Wiring for Two Stage Thermostat
DO NOT connect field wiring to the furnace ignition
control module.
Blower and burner must never be operated without
the blower panel in place.
TYPICAL FIELD WIRING - TWO STAGE
TWO STAGE
THERMOSTAT
Y1
Y2 OUT
R
C
X/L
JUMPER MUST BE IN
TIMER OFF POSITION
CFM/TIMER
BOARD
Y2
Y1
Y
R
W1
W2
G
C
O
X/L
HUM
OUTDOOR
UNIT
Y2
Y1
R
W1
W2
Y2
G
C
X/L
Main power supply to the unit must still be inter-
rupted at the main power disconnect switch before
any service or repair work is to be done to the unit.
Do not rely upon the interlock switch as a main
power disconnect.
