25
Integrated Gas Controller
This unit contains an Integrated Gas Controller (IGC) board.
The IGC control board uses a flue gas pressure switch that
senses pressure drop in the heat exchanger due to the combus-
tion inducer. See Fig. 43.
Fig. 43 — Flue Gas Pressure Switch and Pressure
Sense Tube (Typical Location)
When the thermostat calls for heating, power is sent to W on
the Integrated Gas Controller (IGC) board. An LED (light
emitting diode) on the IGC board turns on and remains on
during normal operation. A check is made to ensure that the
rollout switch and limit switch are closed, and that the pressure
switch is open. If the check was successful, the induced draft
motor is energized. When the pressure in the heat exchanger is
low enough to close the pressure switch, the ignition activation
period begins. Once ignition occurs, the IGC board will contin-
ue to monitor the condition of the rollout switch, the limit
switches, the pressure switch, and the flame sensor. Assuming
the unit is controlled through a room thermostat set for “fan au-
to,” 45 seconds after ignition occurs, the indoor fan motor will
energize, and the outdoor air dampers will open to their mini-
mum position. If the “over temperature limit” opens prior to
the start of the indoor fan blower, the IGC will shut down the
burners, and the control will shorten the 45 second delay to
5 seconds less than the time to trip the limit. For example, if
the limit trips at 37 seconds, the control will change the “fan on
delay” from 45 seconds to 32 seconds. Once the “fan on delay”
has been modified, it will not change back to 45 seconds unless
power is reset to the control. On units with 2 stages of heat, W2
closes and initiates power to the second stage of the main gas
valve when additional heat is required.
When the thermostat is satisfied, W1 and W2 open and the gas
valve closes, interrupting the flow of gas to the main burners. If
the call for W1 lasted less than 1 minute, the heating cycle will
not terminate until 1 minute after W1 became active. If the unit
is controlled through a room thermostat set for fan auto, the in-
door fan motor will continue to operate for an additional
45 seconds, then stop. An LED indicator is provided on the
IGC to monitor operation.
See Fig. 44 for IGC board component layout. Fig. 45 is a typi-
cal IGC control wiring diagram.
Fig. 44 — IGC Board Component Layout
FLUE GA
S
PRE
SS
URE
S
WITCH
FLUE GA
S
PRE
SS
URE
S
EN
S
E TUBE
LOCKING
TAB CONNECTOR
OVERCURRENT FUSE
PROTECTION
REDUNDANT GAS
VALVE RELAY
LOCKING
TAB CONNECTOR
SPADE
CONNECT IGNITOR