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d. Flame-Proving- When the burner flame is proved at the
flame-proving sensor electrode FSE, the furnace control
CPU begins the blower-ON delay period and continues
to hold the gas valve GV open. If the burner flame is not
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 before going to Ignition-Lockout. Lockout will
be reset automatically after three hours, or by momen-
tarily interrupting 115 vac power to the furnace, or by
interrupting 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
furnace control CPU will lock out of Gas-Heating mode
and operate the inducer motor IDM until flame is no
longer proved.
e. 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 terminal
EAC-1 is energized and remains energized as long as the
blower motor BLWM is energized.
f. 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 for a 15-second (040 through 120
sizes) or 5-second (140 size) post-purge period. The
blower motor BLWM and air cleaner terminal EAC-1
will remain energized for 90, 120, 150, or 180 seconds
(depending on the blower-OFF delay selection). The
furnace control CPU is factory-set for a 120-second
blower-OFF delay.
B. Cooling Mode
The thermostat "calls for cooling."
a. Single-Speed Cooling
(See Fig. 27, 50, 52, and 54 for 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/Y2 circuits start the furnace blower motor
BLWM on COOL speed.
The electronic air cleaner terminal EAC-1 is energized
with 115 vac when the blower motor BLWM is operat-
ing.
When the thermostat is satisfied, the R to G-and-Y
circuits are opened. The outdoor unit will stop, and the
furnace blower motor BLWM will continue operating on
the COOL speed for an additional 90 seconds. Jumper
Y/Y2 to DHUM to reduce the cooling off-delay to 5
seconds. (See Fig. 31.)
b. Two-Speed Cooling
(See Fig. 27, 51, 53, 55, and 56 for thermostat connec-
tions.)
The thermostat closes the R to G-and-Y1 circuits for
low-cooling or closes the R to G-and-Y1-and-Y2 circuits
for high-cooling. The R to Y1 circuit starts the outdoor
unit on low-cooling speed, and the R to G-and-Y1 circuit
starts the furnace blower motor BLWM on low-cool
speed (same speed as FAN). The R to Y1-and-Y2
circuits start the outdoor unit on high-cooling speed, and
the R to G-and-Y/Y2 circuits start the furnace blower
motor BLWM on COOL speed.
The electronic air cleaner terminal EAC-1 is energized
with 115 vac whenever the blower motor BLWM is
operating.
When the thermostat is satisfied, the R to G and-Y1 or R
to G and-Y1 and-Y2 circuits are opened. The outdoor
unit stops, and the furnace blower BLWM and electronic
air cleaner terminal EAC-1 will remain energized for an
additional 90 seconds. Jumper Y1 to DHUM to reduce
the cooling off-delay to 5 seconds. (See Fig. 31.)
C. Thermidistat Mode
(See Fig. 50, 51, 52, and 53 for Thermidistat connections.)
The dehumidification output, DHUM on the Thermidistat
should be connected to the furnace control thermostat
terminal DHUM. When there is a dehumidify demand, the
DHUM input is activated, which means 24 vac signal is
removed from the DHUM input terminal. In other words,
the DHUM input logic is reversed. The DHUM input is
turned ON when no dehumidify demand exists. When 24
vac is initially detected by the furnace control on the
DHUM input, the furnace control operates in Thermidistat
mode. If the DHUM input is low or OFF for more than 48
hours, the furnace control reverts back to non-Thermidistat
mode.
The cooling operation described in item 2. above also
applies to operation with a Thermidistat. The exceptions are
listed below:
a. When the R to G-and-Y1 circuit is closed and there is a
demand for dehumidification, the furnace blower motor
BLWM will continue running at low-cool speed (same
speed as FAN).
b. When the R to G-and Y/Y2 circuit is closed and there is
a demand for dehumidification, the furnace blower
motor BLWM will drop the blower speed from COOL to
HEAT for a maximum of 10 minutes before reverting
back to COOL speed. If there is still a demand for
dehumidification after 20 minutes, the furnace control
CPU will drop the blower speed back to HEAT speed.
This alternating 10-minute cycle will continue as long as
there is a call for cooling.
c. When the "call for cooling" is satisfied while there is a
demand for dehumidification, the cooling blower-off
delay is decreased from 90 seconds to 5 seconds.
D. Continuous Blower Mode
When the R to G circuit is closed by the thermostat, the
blower motor BLWM will operate on continuous-blower
speed (can be adjusted to FAN, HEAT, or COOL speed) at
the thermostat. Factory default is FAN speed. Terminal
EAC-1 is energized as long as the blower motor BLWM is
energized.
During a call for heat, the blower BLWM will stop during
igniter warm-up (17 seconds), ignition (7 seconds), and
blower-ON delay (66 or 45 seconds for 040 through 120
sizes or for 140 size), allowing the furnace heat exchangers
to heat up more quickly, then restarts at the end of the
blower-ON delay period at HEAT speed.
In heating, the furnace control CPU will hold the blower
motor BLWM at HEAT speed during the selected blower-
OFF delay period before reverting to continuous-blower
speed.
When the thermostat "calls for low-cooling", the blower
motor BLWM will switch to operate at low-cool speed
(same speed as FAN). When the thermostat is satisfied, the
blower motor BLWM will operate an additional 90 seconds
on low-cool speed (same speed as FAN) before reverting
back to continuous-blower speed.
When the thermostat "calls for high-cooling", the blower
—47—
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