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Preface
Air Conditioning and heating service technicians
must have a working knowledge of basic electrical and
refrigeration service procedures. In order to service
gas furnaces, a thorough understanding of the units
sequence of operation is essential. This publication is
Contents
Model Evolution ..........................................................................................................................................................
Model Nomenclature ..................................................................................................................................................
Component Identification - UD/ DD-R Models ......................................................................................................
Component Identification - UY/ DY-R Models .......................................................................................................
Integrated Furnace Controls (I.F.C.) ............................................................................................................................
Self Diagnostic Features 50A50 and 50A51 ...............................................................................................................
Integrated Furnace Control Timing ............................................................................................................................
Abnormal Furnace Operation - 50A50 and 50A51 ....................................................................................................
Single Stage 50A50 Sequence of Operation ..............................................................................................................
Wiring Schematic - Single Stage 50A50 Integrated Furnace Control ......................................................................
Two Stage 50A51-405 Sequence of Operation ..........................................................................................................
Wiring Schematic - Two Stage Heat 50A51-405 Integrated Furnace Control .........................................................
Two Stage Variable Speed Sequence Of Operation ..................................................................................................
Wiring Schematic - Two Stage Variable Speed 50A51-505/50A51-506 Integrated Furnace Control .....................
Integrated Control Quick Reference ...........................................................................................................................
2 Variable Speed Furnace Motor Quick Check ...............................................................................................
Schematic - Motor Control Board ..............................................................................................................................
Flame Rectification Principle - Measurement ...........................................................................................................
Flame Current Tester/Simulator .................................................................................................................................
Combustion Air Pressure Switch Check - Measurement .........................................................................................
Furnace Pressure Switch Settings ..............................................................................................................................
Gas Valves ....................................................................................................................................................................
Note: This publication is general in nature and is intended for
INSTRUCTIONAL PURPOSES ONLY. It is not to be used for
equipment selection, application, installation, or specific service
procedures.
based on White-Rogers controls and provides the
narrative and schematic drawingsnecessary to
provide this understanding for thesefurnaces. Also
included is a description of operating principles of
different ignition systems.
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continued
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