analog to digital converter . . . . . . . . . . . . . . . 4 - UPGNet

351579-YTS-B-0608Pressure Switch - The pressure switch closes on adrop below a specific pressure. On a call for heat, theICB checks the pressure switch for open state before itenergizes the draft motor. If it is closed, then the ICB willlock out the furnace and flash a code (Table 7). If open,then the ICB will energize the draft motor and verify thatthe switch closes before initiating the purging and ignitionsequence. If at any time during furnace operationthe pressure switch opens, then the ICB will de-energizethe gas valve and monitor the pressure switch. If thepressure switch closes and the call for heat still exists,then the ICB will retry the purging and ignition sequence.Rollout Switch - This temperature sensitive switch ismounted on the burner assembly top shield. In the eventof the flame spilling out into the burner assembly areaand the rollout switch opens, the ICB will close the gasvalve and flash a code (Table 7). The ICB cannot bereset automatically as the roll out switch is of the manualreset type.Flame Sense Circuit - The flame sensor is mounted onthe left hand side of the burner assembly and is positionedsuch that the flame from the first burner from theleft side surrounds the tip of the sensor. On a call forheat the ICB checks for the flame sense circuit to beopen. If open, then the ICB initiates the purging and ignitionsequence. Once the flame is present, the ICB monitorsthe flame sense circuit for flame stability. If the flameis unstable or lost completely, then the ICB will immediatelyclose the gas valve. The ICB will retry the purgingand ignition sequence. If the flame is unstable or lostmore than 5 times during the same call for heat, then theICB will lock out that module and flash the appropriatecode.Flash Codes - The ICB will initiate a flash code associatedwith errors within the ignition and gas control system.See Table 7 for the list of codes for the ICB.Table 7: Ignition Control Board Flash Codes12. Gas Heat Two-Stage Module: The arrangement and operationfor two stage modules is similar to the single stagemodules except that the gas valve and the ignition controlare replaced with a two stage gas valve and a two stageignition control. For faster heat exchanger warm up, theICB will automatically run each module on high fire for 30seconds given a low fire only call for heat. Because the useof two stage modules is restricted to modulating gas heat,there is a Modulating Furnace Control (MFC) with a dedicateddischarge air temperature sensor added between theUCB and the two stage ignition control for each installedmodule.13. Gas Heat Modulating Module: The modulating module issignificantly different from the single and two stage modules.It consists of one module broken into two systems.Each system has its own complement of gas valve, ignitioncontrol, draft motor and safety devices. The burner orificemanifold is internally sealed such that the left three burnersare supplied with fuel from one two stage gas valve whilethe right two burners are supplied with fuel by a second twostage gas valve. This modulating module is always presenton a modulating furnace with additional two stage modulesinstalled as required by the application.Modulating Furnace Control - The Modulating FurnaceControl (MFC) is designed to accept a W1 and W2 callfor heat and then control up to 8 stages of gas heat forup to 17 steps of gas heat input rates. It is configurablefor air tempering in free cooling mode without any inputfrom the UCB when in constant volume air flow that is ator above the minimum air flow for heating. It uses configurablevalues and sensor input to determine the amountof heat that is required to meet the heating load up to themaximum heat output that is installed. Below is thesequence of steps for the three different systems available.The LF and HF designations represent the low fireand high fire gas valve signal for each system, SeeTable 8. Modulating Gas Furnace control board failurecodes are found in Table 9.Flash CodeDescriptionHeart Beat Normal Operation1 Flash Not Applicable2 Flashes Pressure / Centrifugal Switch Open with Inducer On3 FlashesPressure / Centrifugal Switch Closed with InducerOff4 Flashes Lock Out From Too Many Failed Ignition Tries5 Flashes Lock Out From Too Many Flame Losses6 Flashes High Temperature Switch Open7 Flashes Rollout Switch Open8 Flashes Flame Present With Gas Off9 Flashes Exceeded Max Limit Trips In One Call For Heat (5)10 Flashes Gas Valve Stuck Off or OnJohnson Controls Unitary Products 23