Step 12—Start-up, Adjustment, and Safety Check
GENERAL
NOTE:
Proper polarity must be maintained for 115-v wiring. If
polarity is incorrect, control center status indicator light will flash
rapidly and furnace will not operate.
The furnace must have a 115-v power supply properly connected
and grounded. Proper polarity must be maintained for correct
operation. Thermostat wire connections at R, W, C, and Y must be
made at the 24-v terminal block on the control board. The gas
service pressure must not exceed 0.5 psig (14-in. wc), but must be
no less than 0.16 psig (4.5-in. wc).
Before operating the furnace, check each manual reset switch for
continuity. If necessary, press the button to reset the switch.
The blower compartment door must be in place to complete the
115-v circuit to the furnace.
This furnace is equipped with 2 manual reset limit switches in
the gas control area. The switches will open and shut off
power to the gas valve if a flame rollout or an overheating
condition occurs in the gas control area. DO NOT bypass the
switches. Correct inadequate combustion air supply problem
and reset the switches.
SEQUENCE OF OPERATION
Using the schematic diagram shown in Fig. 16, follow the
sequence of operation through the different modes. Read and
follow the wiring diagram very carefully.
Furnace control must be grounded for proper operation or
control will lockout. Control is grounded through green wire
routed to gas valve and burner bracket screw.
NOTE:
If there is a power interruption and any thermostat call,
the control will initiate a 90-sec blower only on period before
starting another cycle.
1. Heating mode
When the thermostat "calls for heat," R-W circuit closes. The
furnace control performs a self-check, verifies the pressure
switch contacts are open, and starts the inducer motor.
a. Prepurge period—As the inducer motor comes up to speed,
the pressure switch contacts close to begin a 15-sec
prepurge period.
b. Igniter warm-up—At the end of the prepurge period, the
igniter is energized for a 17-sec igniter warm-up period.
c. Ignition sequence—When the igniter warm-up period is
completed, the gas valve opens, permitting gas flow to the
burners where it is ignited. After 5 sec, the igniter is
de-energized and a 2-sec flame-sensing period begins.
d. HUM terminal is energized with the gas valve. See
Accessories in Electrical Connections section.
e. Flame-sensing—When burner flame is sensed, the control
begins the blower on delay period and continues holding
the gas valve open. If burner flame is not sensed, the
control closes the gas valve and repeats the ignition cycle.
NOTE:
Ignition sequence will repeat 3 additional times before a
lockout occurs. Lockout automatically resets after 3 hrs, or can be
manually reset by turning 115v off (not at thermostat) for 3 sec
minimum, then on again.
f. Blower on delay—Forty-five sec after burner flame is
proven, the blower motor is energized on heating speed.
Simultaneously, the humidifier and electronic air cleaner
terminals (HUM and C
OM
-24V for humidifier, EAC-1 and
EAC-2 for electronic air cleaner) are energized.
g. Blower off delay—When the thermostat is satisfied, the
circuit between R and W is broken, de-energizing the gas
valve and stopping gas flow to the burners. The blower
motor, and EAC remain energized for 135 sec.
h. Post-purge—The inducer motor remains energized 5 sec
after the burners are extinguished.
2. Cooling mode
When the thermostat "calls for cooling," R-G and R-Y circuits
close. The R-Y circuit starts the outdoor condensing unit and
combined R-Y and R-G circuits start the furnace blower motor
on cooling speed. The EAC-1 terminal is energized with 115v
whenever the blower is operating on cooling speed.
When the thermostat is satisfied, R-G and R-Y circuits are
broken. Furnace blower and EAC continue operating on
cooling speed for an additional 90 sec.
3. Continuous blower mode
NOTE:
EAC-1 terminal is energized with 115v whenever blower
is operating.
When the R-G circuit is made, the blower motor operates on
heating speed. During a call for heat, the blower stops,
allowing the furnace heat exchangers to heat up more quickly,
then restarts at the end of the 45-sec blower on delay period.
The blower reverts to continuous operation after the heating
cycle is completed.
When the thermostat "calls for cooling," the blower operates
on cooling speed. When the thermostat is satisfied, the blower
operates an additional 90 sec before reverting back to con-
tinuous operation on heating speed.
Table 6—Electrical Data
UNIT SIZE
VOLTS—
HERTZ—
PHASE
OPERATING VOLTAGE RANGE
MAXIMUM
UNIT AMPS
MINIMUM
WIRE GAGE
MAXIMUM WIRE
LENGTH FT‡
MAXIMUM
FUSE OR CKT BKR
AMPS†
Maximum*
Minimum*
050-08
115—60—1
127
104
6.6
14
42
15
050-12
115—60—1
127
104
8.1
14
34
15
070-08
115—60—1
127
104
6.7
14
42
15
070-12
115—60—1
127
104
8.4
14
33
15
095-12
115—60—1
127
104
9.2
14
30
15
095-16
115—60—1
127
104
10.2
14
28
15
115-16
115—60—1
127
104
10.1
14
28
15
115-20
115—60—1
127
104
13.3
12
33
20
135-20
115—60—1
127
104
14.3
12
31
20
* Permissible limits of the voltage range at which the unit will operate satisfactorily.
† Time-delay type is recommended.
‡ Length shown is as measured 1 way along wire path between unit and service panel for maximum 2 percent voltage drop.
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