Carrier WeatherMaker 48FC04-07 Installation Instructions Manual

25Integrated Gas ControllerThis unit contains an Integrated Gas Controller (IGC)board. The IGC control board uses a flue gas pressure switchthat senses pressure drop in the heat exchanger due to thecombustion inducer. See Fig. 43.Fig. 43 — Flue Gas Pressure Switch and PressureSense Tube (Typical Location)When the thermostat calls for heating, power is sent to Won the Integrated Gas Controller (IGC) board. An LED (lightemitting diode) on the IGC board turns on and remains onduring normal operation. A check is made to ensure that therollout switch and limit switch are closed, and that the pres-sure switch is open. If the check was successful, the induceddraft motor is energized. When the pressure in the heat ex-changer is low enough to close the pressure switch, the igni-tion activation period begins. Once ignition occurs, the IGCboard will continue to monitor the condition of the rolloutswitch, the limit switches, the pressure switch, and the flamesensor. Assuming the unit is controlled through a room ther-mostat set for “fan auto,” 45 seconds after ignition occurs, theindoor fan motor will energize, and the outdoor air damperswill open to their minimum position. If the “over temperaturelimit” opens prior to the start of the indoor fan blower, theIGC will shut down the burners, and the control will shortenthe 45 second delay to 5 seconds less than the time to trip thelimit. For example, if the limit trips at 37 seconds, the controlwill change the “fan on delay” from 45 seconds to 32 sec-onds. Once the “fan on delay” has been modified, it will notchange back to 45 seconds unless power is reset to the con-trol. On units with 2 stages of heat, W2 closes and initiatespower to the second stage of the main gas valve when addi-tional heat is required.When the thermostat is satisfied, W1 and W2 open and thegas valve closes, interrupting the flow of gas to the mainburners. If the call for W1 lasted less than 1 minute, the heat-ing cycle will not terminate until 1 minute after W1 becameactive. If the unit is controlled through a room thermostat setfor fan auto, the indoor fan motor will continue to operate foran additional 45 seconds, then stop. An LED indicator is pro-vided on the IGC to monitor operation.See Fig. 44 for IGC board component layout. Fig. 45 is atypical IGC control wiring diagram.Fig. 44 — IGC Board Component LayoutFLUE GASPRESSURESWITCHFLUE GASPRESSURESENSE TUBELockingTab ConnectorOvercurrent FuseProtectionRedundant GasValve RelayLockingTab ConnectorSpadeConnect Ignitor