where it is ignited. After 5 sec, ignitor is de-energized and
a 2-sec flame-sensing period begins.
HUM terminal on control center is energized with gas
valve. See Accessories - Humidifier section.
4. Flame sensing—When burner flame is sensed, control
begins blower on delay period and continues holding gas
valve open.
If burner flame is not sensed, control center de-energizes
gas valve and ignition sequence is repeated.
NOTE: Ignition sequence repeats 3 additional times before a
lockout occurs. Lockout automatically resets after 3 hr or can be
manually reset by turning off 115-v (not at thermostat) for 3 sec
minimum, then turning it on again.
5. Blower on delay—Sixty sec after burner flame is proven
(40 sec if jumper has been cut for 140 size unit in downflow
orientation), blower motor is energized on heating speed.
Simultaneously, electronic air cleaner terminal EAC-1 is
energized.
6. Blower off delay—When thermostat is satisfied, circuit
between R-W is opened, de-energizing gas valve (stopping
gas flow to burners) and humidifier. Blower motor and
electronic air cleaner remains energized 90, 135, 180, or
225 sec (depending on blower off time selection). Furnace
is factory shipped set for a 135-sec blower off delay.
7. Post purge—inducer motor remains energized 15 sec after
burners are extinguished (5 sec if jumper has been cut for
140 size unit in downflow orientation).
B. COOLING MODE
When thermostat calls for cooling, R-G and R-Y circuits close.
R-Y circuit starts outdoor condensing unit, and combined R-Y and
R-G circuit starts furnace blower motor on cooling speed. Elec-
tronic air cleaner EAC-1 terminal is energized with 115–v when-
ever blower is operating.
When thermostat is satisfied, R-G and R-Y circuits are opened,
furnace blower continues operating on cooling speed for an
additional 90 sec.
C. CONTINUOUS BLOWER MODE
When R-G circuit is made, blower motor operates on heating
speed.
NOTE: Electronic air cleaner EAC-1 terminal is energized with
115–v whenever blower is operating.
If a call for heat (R-W) occurs while thermostat is in continuous
blower mode, blower stops to allow furnace heat exchangers to
heat up more quickly, then restarts at end of blower on delay
period of 60 sec (40 sec if jumper has been cut for 140 size unit in
downflow orientation).
COMBUSTION
AIR
VENT
VENT
A
A93056
Fig. 36—Concentric Vent and Combustion-Air Roof
Termination (Dimension “A” is Touching or 2-in. Maximum
Separation)
Fig. 38—Sidewall Termination of 12 in. or Less
(Dimension “A” is Touching or 2-in. Maximum Separation)
A96129
A
COMBUSTION AIR
COMBUSTION AIR
VENT
COMBUSTION AIR
VENT
A
VENT
1″ MAXIMUM
(TYP)
A93057
Fig. 37—Concentric Vent and Combustion-Air Side
Termination (Dimension “A” is Touching or 2-in. Maximum
Separation)
VENT
A
COMBUSTION AIR
COMBUSTION AIR
A96130
Fig. 39—Sidewall Termination of More than 12 in.
(Dimension “A” is Touching or 2-in. Maximum Separation)
—32—
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