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035-15241-003 Rev. A (201)
WIRING DIAGRAM
PS
FS
YEL
BDSS
BLK
BLK
115V
WHT
TO
A/C
Y
W
R
G
T'STAT
= Transformer
XFMR
= Hot Surface Ignitor
IGN
= Capacitor
CAP
= Vent Motor
VM
= Gas Valve
GV
= Flame Sensor
FS
= Blower Door Safety Switch
BDSS
= Rollout Switch
ROS
= Limit Switch
LS
= Pressure Switch
PS
= Wall thermostat
T'STAT
PRE-OPERATIONAL CHECKS
SHOCK HAZARD - Be sure electrical power to
furnace is turned off before performing the pre-
operational checks.
1.
Be sure that the furnace is equipped for the type of gas
being supplied to the furnace. See unit rating plate. If LP
(propane) gas is to be used, make sure that the fur-
nace has been properly converted.
2.
Manually spin circulating air blower wheel to ensure that
it turns freely and does not strike the blower housing.
3.
Was the gas piping tested and/or purged of air then
checked for leaks? See instructions for gas piping. Even
the smallest leak must be eliminated before attempting
to light the furnace.
SEQUENCE OF OPERATION
These furnaces are equipped with an electric hot surface
burner ignition system. In response to a call for heat by the
room thermostat, a hot glowing ignitor lights the burners at
Unitary Products Group
DISCONNECT THE ELECTRIC POWER BEFORE SERVICING.
RED
RED
ROS
ROS
LS
GV
10
11 12
Y
7
8
9
W
4
5
6
R
1
2
3
A
G
1 2 3
C
XFMR
BRN
CAP
BRN
BLOWER
Factory internal wiring shown solid. If any of the original
wire supplied with this unit must be replaced, it must be
replaced with Type 105º C thermoplastic or its equivalent.
ROS
VM
PUR
PUR
COOL
HEAT
PARK
PARK
L1
XFMR
EAC
HUM
4
B
IGN
BLU
BLU
COM
HI
MH
ML
LO
the beginning of each operation cycle. The burners will con-
tinue to operate until the thermostat is satisfied at which time
all burner flame is extinguished. During the off cycle no gas is
consumed. With the room thermostat set below room temper-
ature and with the electrical power and gas supply to the fur-
nace on, the normal sequence of operation is as follows:
1.
When the room temperature falls below the setting of the
room thermostat, the thermostat energizes the furnace
control board.
2.
When the furnace control board is activated, the vent
blower is turned on. A circuit is also made through the
normally open pressure switch contacts.
3.
As the vent blower increases in speed, the contacts of
the pressure switch will close and complete the electrical
circuit to the ignitor.
4.
During the next 30 seconds, the vent blower will bring
fresh air into the heat exchanger and the ignitor will
begin to glow. At the end of this period, the gas valve will
open and the burners will light.
5.
After the burners light, a separate sensor acts as a flame
probe to check for the presence of flame. As long as a
flame is present, the system will monitor it and hold the
gas valve open.
IGN
BLOWER
P-2B
P-4B
COM
HI
COOL
MH
HEAT
ML
PARK
LO
PARK
P-1B
P-3B
CAP
VM
L1
XFMR
P-2A
FS
NEU
115V
XFMR
24V
P-6A
P-5A
ROS
ROS
ROS
P-11A
P-8A
P-7A
P-10A
P-3A
PS
LS
P-1A
P-9A
GV
P-12A
19
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