# 45465K005
Page 20
Sequence of Operation (G1D80BR and G1D80BT
Models)
Heating
During a call for heat the thermostat closes the R-W
circuit of the control board. The control board verifies limit
switches are closed and pressure switch is open. The
induced draft blower relay closes causing the blower to
run. As vent pressure is developed by the induced draft
blower, the pressure switch closes. After a 15-second pre-
purge, the control energizes the hot surface ignitor. After
the 7-second warmup time, the control energizes the main
gas valve causing the main burners to ignite. The hot
surface ignitor is de-energized 3 seconds after the main
valve opens. If flame is sensed during this time the main
valve remains energized and the control starts the
30-second heat blower “on” delay.
As heating demand is met, the thermostat de-energizes the
R-W circuit. The control de-energizes the main valve
causing the burners to shut off. The induced draft blower
shuts off after a 15-second post-purge delay. The circulating
air blower will continue to operate until the user-selectable
heat blower “off” delay expires. The control return to standby
mode once the heat blower “off” delay expires.
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”
During a fan “on” call, the thermostat energizes the R-G
circuit of the control board, immediately causing the fan to
energize the heat speed. The fan remains energized as
long as the thermostat calls for fan “on” operation.
If a call for heat is energized during a fan “on” call, the fan
continues to operate at the heat speed. If a call for cooling is
energized during a fan “on” call, the fan switches to cooling
speed.
At the end of the fan “on” call the thermostat de-energizes
the R-G circuit of the control, causing the fan to be de-
energized immediately.
OPERATION
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.
Sequence of Operation (G2D80CR and G2D80CT
Models)
Heating
When the control is in standby mode, it continually moni-
tors thermostat input, rollout switch, and flame sense.
On a call for 1
st
stage heat, W1 and R are connected. The
control verifies the limit switch is closed and both low and
high pressure switches are open. The control always starts
on low-fire and ignores 2
nd
stage call for 30 seconds.
The induced draft blower is energized on high speed and
waits for the low pressure switch to close. The inducer
remains on high speed and begins a pre-purge period
when the low pressure switch closes. After a 15-second
pre-purge, the control energizes the hot surface igniter for
a period of 7 seconds (15 seconds on retries) before the
gas valve is energized on 1
st
stage and main burners
ignite. After a 30-second blower “on” delay, the control
energizes the low heat circulating air blower. Fifteen
seconds after the circulating air blower energizes, the
combustion air blower switches to low speed and runs at
that speed until the thermostat is satisfied.
If the 1
st
stage is not sufficient to satisfy the heating
demand, the room thermostat initiates call for the 2
nd
stage heating (W1 and W2). The control energizes the
combustion blower on high speed and confirms the high-
fire pressure switch contacts are closed. If the contacts
are closed, the gas valve energizes on the 2
nd
stage and
the high-heat circulating air blower is energized.
If the automatic heat staging option is being used (see
Single Stage Thermostat Operation
on page 17), the
furnace does not switch to 2
nd
stage heat in response to a
call from the thermostat but instead operates at 1
st
stage
heat for the duration of the selected time before automati-
cally switching to 2
nd
stage heat.
