Residential Gas Furnace Operation - HVAC.Amickracing

PrefaceAir Conditioning and heating service techniciansmust have a working knowledge of basic electrical andrefrigeration service procedures. In order to servicegas furnaces, a thorough understanding of the unitssequence of operation is essential. This publication isbased on White-Rogers controls and provides thenarrative and schematic drawingsnecessary toprovide this understanding for thesefurnaces. Alsoincluded is a description of operating principles ofdifferent ignition systems.ContentsModel Evolution .......................................................................................................................................................... 3Model Nomenclature .................................................................................................................................................. 4Component Identification – ✽UD/✽DD-R Models ...................................................................................................... 5Component Identification – ✽UY/✽DY-R Models ....................................................................................................... 6Integrated Furnace Controls (I.F.C.) ............................................................................................................................ 7Self Diagnostic Features 50A50 and 50A51 ............................................................................................................... 9Integrated Furnace Control Timing ............................................................................................................................ 10Abnormal Furnace Operation – 50A50 and 50A51 .................................................................................................... 11Single Stage 50A50 Sequence of Operation.............................................................................................................. 14Wiring Schematic – Single Stage 50A50 Integrated Furnace Control...................................................................... 15Two Stage 50A51-405 Sequence of Operation .......................................................................................................... 16Wiring Schematic – Two Stage Heat 50A51-405 Integrated Furnace Control ......................................................... 17Two Stage Variable Speed Sequence Of Operation .................................................................................................. 18Wiring Schematic – Two Stage Variable Speed 50A51-505/50A51-506 Integrated Furnace Control ..................... 19Integrated Control Quick Reference ........................................................................................................................... 20Furnace ECM TM 2 Motor Operation ............................................................................................................................. 21ECM TM 2 Variable Speed Furnace Motor Quick Check ............................................................................................... 22Schematic – Motor Control Board .............................................................................................................................. 24Flame Rectification Principle – Measurement ........................................................................................................... 25Flame Current Tester/Simulator ................................................................................................................................. 26Combustion Air Pressure Switch Check – Measurement ......................................................................................... 27Furnace Pressure Switch Settings .............................................................................................................................. 28Gas Valves .................................................................................................................................................................... 29✽ Models maybe an A or T or FcontinuedNote: This publication is general in nature and is intended forINSTRUCTIONAL PURPOSES ONLY. It is not to be used forequipment selection, application, installation, or specific serviceprocedures.1