-9
Step 3--Purge Gas Lines
FIRE AND EXPLOSION HAZARD
Failure to %llow this warning could result in a fire, explosion,
personal inju W, or death
Never pm'ge a gas line into a combustion chamber Never test
for gas leaks with an open flame Use a commercially
available soap solution made specifically for the detection of
teaks to check all connections
If not previousiy done, purge lines after all connections have been
made and check for teaks.
Step 4--Sequence of Operation
m
FURNA(E MAY NOT OPERATE
Failm'e to _bltow this caution may result in fi.u'nace operation
stopping and water pipes t'reezing during cold weather.
Fu*nace control must be grounded fbr proper operation, or
control will lock out. Control is grounded through
green@ellow wire routed to gas valve and burner box screw.
Using schematic diagram, %l!ow sequence of operation through
different modes (See Fig. 30.) Read and follow wiring diagram
carefldly
NOTE: Ifa power inten-uption occurs during a call fbr heat (W),
the contlol will start a 90-second blower-only ON period two
seconds after power is restored, if the fl'lermostat is still calling for
gas heating. The red LED light will flash code 12 during the
90=second period, after which the LED will be ON continuous, as
tong as no faults are detected. After the 90-second period, the
furnace will respond to the thermostat normally
The blower door must be installed fbr power to be conducted
through the blower door interlock switch ILK to the furnace
control (PU.. transformer TRAN, inducer motor IDM, blower
motor BLWM, hot=surf:ace igniter HSI, and gas valve GV.
HEATING MODE
(See Fig. 27 for thermostat connections.)
The wall thermostat "calls for heat", closing the R to W
circuit. The Nrnace contlol perfbm_s a self-check, verifies the
pressure switch contacts PRS are open, and starts the inducer
motor IDM.
a. Inducer Prepurge Period- As the inducer motor IDM
comes up to speed, the pressure switch contacts PRS close,
24 vac power is supplied £br a field installed humidifier at
the HUM terminal and the control begins a 15-second
prepurge period.
b. Igniter Warm-Up- At the end of the prepurge period, the
Hot=Surface Igniter HSI is energized fbr a 17-second
igniter warm=up period.
c. Trial-Nr-Ignition Sequence= When the igniter warm=up
period is completed the main gas valve relay contacts GVR
close to energize the gas valve GV, the gas valve opens.
The gas valve GV permits gas flow to the burners where it
is ignited by the Hot Surface Igniter HSI. Five seconds after
the GVR closes, a 2-second flame period begins. The HSI
igniter will remain energized until the flame is sensed or
until the 2-second flame proving period begins.
d. Flame-Proving- When the burner flame is proved at the
flame-proving sensor eleckode FSE, the ft/rnace contlol
CPU begins the blower=ON delay period and continues to
hold the gas valve GV open. If the burner flame is not
37
proved within two seconds, the control CPU will close the
gas valve GV, and the control CPU will repeat the ignition
sequence for up to three more Trials-For=Ignition befbre
going to Ignition=Lockout Lockout will be reset attto-
matically after three hours, by momentarily interrupting
115 vac power to the furnace, or by internlpfing 24 vac
power at SEC1 or SEC2 to the furnace control CPU (not at
W, G, R, etc.)
If flame is proved when flame should not be present, the
fhrnace control CPU will lock out of Gas-Heating mode
and operate the inducer motor IDM until flame is no longer
proved.
Blower-On Delay= If the burner flame is proven, the
blower motor is energized on HEAT speed 66 seconds (040
through 120 sizes) or 45 seconds (140 size) after the gas
valve GV is energized.
Simultaneously, the electronic air cleaner tmlninal EAC=I
is energized and remains energized as tong as the blower
motor BLWM is energized.
Blower-Off Delay- When the thermostat is satisfied, the
R=to=W circuit is opened, de-energizing the gas valve GV,
stopping gas flow to the burners, and de-energizing the
humidifier terminal HUM. The inducer motor IDM will
remain energized fbr a 15=second (040 through 120 sizes)
or 5-second (140 size) post=purge period. The blower motor
BLWM and air cleaner terminal EAC=I will remain ener-
gized for 90, 120, 150, or 180 seconds (depending on the
blower=OFF delay selection). The Nrnace control CPU is
fhctory-set for a 120=second blower=OFF delay.
COOLING MODE
(See Fig. 27 %r thermostat connections)
The thermostat closes the R-to=G=and-Y circuits The R-to=Y
circuit starts the outdoor unit, and the R=to=G and Y circuits start
the fhrnace blower motor BLWM on COOL speed.
The electronic air cleaner terminal EAC=I is energized with 115
vac when the blower motor BLWM is operating.
When the them_ostat is satisfied, the R-to=G=and-Y circuits are
opened. The outdoor unit will stop, and the fhmace blower motor
BLWM will continue operating on the COOL speed for an
additional 90 seconds Cut jumper J2 to reduce the cooling
off-delay to 5 seconds.
CONTINUOUS BLOWER MODE
When the R=to-G circuit is closed by the thermostat, the blower
motor BLWM will operate on continuous=blower speed (same as
HEAT speed). Terminal EAC=I is energized as tong as the blower
motor BLWM is energized.
During a "call fbr heat," the blower BLWM will stop during igniter
warm=up (17 seconds), ignition (7 seconds), and blower-ON delay
(66 or 45 seconds fbr 040 through 120 sizes or fbr 140 size),
allowing the fimaace heat exchangers to heat up more quickly, then
restarts at the end of fl_e blower-ON delay period at HEAT speed.
In heating, the fl/rnace control CPU will continue running the
blower motor BLWM at HEAT speed after the selected blower-
OFF delay period is completed.
When the thermostat "calls fbr cooling", the blower motor BLWM
will operate at COOL speed. When the thermostat is satisfied, the
blower motor BLWM will operate an additional 90 seconds on
COOL speed befbre reverting back to HEAT speed. Jumper J2 can
be cut to reduce the cooling off=delay to 5 seconds. (See Fig. 3!.)
When the R=to-G circuit is opened, the blower motor BLWM will
continue operating fbr an additional 5 seconds, if no other function
requires blower motor BLWM operation.
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