# 45465K005 Page 21
When the 2
nd
stage heat is satisfied, the control shuts off
the gas valve and runs the combustion blower for a post-
purge period of 15 seconds. The circulating air blower
continues to run according until the selected blower “off”
delay time (factory shipped at 120 seconds) ends.
In the event the unit loses ignition, the control will attempt
to recycle up to five times before it goes into a 1-hour
lockout. Lockout may be manually reset by removing
power from the control for more than 1 second or remov-
ing the thermostat call for heat for more than 3 seconds.
If during a heating cycle the limit control senses an
abnormally high temperature and opens, the circulating air
blower is energized on high speed and continues to run
while the limit is still open.
Fan “On”
A call for fan from the thermostat closes R to G on the
control board. The control waits for a 1-second thermostat
debounce delay before responding by energizing the low
heat speed blower. When the call for fan is turned off, the
control de-energizes the blower.
Cooling
During a call for cooling, the thermostat energizes the R-Y
circuit of the control board. After a 1-second cooling “on”
delay, the control energizes the cooling fan speed. If the fan
is already energized, it remains running and does not de-
energize for the 1-second cooling fan “on” delay.
The call for cooling has priority over continuous fan
operation while a call for heating has priority over both a
call for cooling or continuous fan. Ignition lockouts for any
reason do not affect cooling operation.
As cooling demand is met, the thermostat de-energizes
the R-Y circuit of the control board. After a 60-second
cooling “off” delay, the control de-energizes the cooling
speed fan. At the end of the cooling “off” delay period, the
control returns to the standby mode.
Controls
Following is a description of the operation of some of the
controls used in this furnace. All models use one of each
control, except as noted.
Pressure Switch
The pressure switch is a normally open switch that monitors
combustion air flow. Inadequate air flow resulting from
excessive venting system restriction or a failed combustion
blower will cause the switch to remain open. G2D80CR and
G2D80CT models have two pressure switches.
Rollout Switch
The rollout switch is a normally closed switch that opens
when abnormal temperatures exist in the burner area. This
can be caused by a restricted heat exchanger causing main
burner flame to “roll out” into vestibule area or burner box.
This switch must be manually reset by pushing the button
on top to restore furnace operation. All four models
described in this manual incorporate two rollout switches.
Primary Limit Control
This is a normally closed control that opens if abnormally
high circulating air temperatures occur. It is an automatic
reset control.
Auxiliary Limit Control
This is a normally closed control, located on the circulat-
ing air blower housing, that opens under abnormal “re-
verse air flow” conditions that could occur in a counterflow
or horizontal installation if the circulating air blower fails. It
is an automatic reset control.
Interlock (Blower Door) Switch
When the blower door is removed, the interlock switch
breaks the power supply to the burner controls and blower
motor. The switch operation must be checked to confirm it
is operating correctly.
Integrated Ignition/Blower Control Board
The integrated ignition/blower control board operates all
functions of the furnace and any accessories connected to
it. These models feature user-selectable blower “off” delay
times (60, 90, 120, and 180 seconds) that are factory set to
provide a 120-second blower “off” delay on heating (see
connection diagram on either page 28 or page 30).
Refer to the furnace wiring diagram while using the
following procedure to change motor speed:
1. Turn off electrical power to the unit.
2. Connect the desired speed tap for cooling on the
control board.
3. For heating speed, check the temperature rise and, if
necessary, adjust blower speed tap to maintain
temperature rise within the range shown on furnace
rating plate.
To use the same speed tap for both heating and
cooling, install a piggyback terminal on the speed tap
using a short jumper. Wire 1/4" quick connect termi-
nals on both ends to jumper the “HEAT” and “COOL”
speed on the control board.
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