Trane RT-SVX10C-EN Gas Heating Sequence of Operation, Fenwal Ignition System, Unit Start-Up

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Lead/Lag Operation

When Lead/Lag is enabled, each time the system cycles af- ter having stages 1 and 2 "On", "Stage 2" (K11 on SCM or K3 on MCM) and the corresponding condenser fan output "2A" will start first. The compressor module cycles the compressors "On" and "Off" to keep the zone temperature within the cooling setpoint deadband. The condenser fans are cycled "On" and "Off" to maintain the saturated refriger- ant temperature within the specified controlband.

Units equipped with 100% modulating exhaust

The exhaust dampers are controlled through an Exhaust/ Comparative Enthalpy Module (ECEM). The ECE module receives input form a space transducer and modulates the exhaust dampers to maintain the space pressure to within the specified setpoint controlband.

Gas Heating Sequence of Operation

Standard Two Stage Gas Furnace

The control system for the rooftop units are wired to ensure that the heating and cooling do not occur simultaneously. Refer to the wiring diagram that shipped with the unit while reviewing the following sequence of operation.

Fenwal Ignition System

(235 & 350 MBH Natural Gas)

When a heating requirement exists, the Rooftop Module (RTM) starts the supply fan and sends a request for heat to the Heat Module. The Heat Module closes K11 contacts and starts the combustion blower motor (4B11). The com- bustion blower motor starts on low speed through the nor- mally closed combustion fan relay (4K33) contacts. The heat module also closes K12 contacts. Power is then sup- plied through the supply air flow switch (4S38), the com- bustion air flow switch (4S25), the high limit cutout (4S26), and finally through the normally closed sequencing time delay (4DL6) contacts to the pre-purge time delay relay (4DL5). The Fenwal ignition control board (4U18), the 60 second sequencing time delay relay (4DL6), and the com- bustion blower relay (4K33) will not energize until the pre- purge timer (4DL5) closes its contacts. Once closed, the Fenwal ignition control board (4U18) energizes the 1st stage solenoid on the gas valve (4L15), the interlock relay (4K32), and the ignition electrode (4E1). A second set of normally open timed closed contacts on the pre-purge timer (4DL5) are wired into the 1U50 heat fail input in se- ries with a normally closed set of contacts on the interlock relay (4K32). When the commonly open contacts on the in- terlock relay (4K32) closes, it will maintain an electrical path for the ignition control board (4U18) and subsequent controls after the pre-purge timer (4DL5) is de-energized by the sequencing time delay relay (4DL6). The normally open contacts on the pre-purge time delay relay (4DL5) will open in the 1U50 heat fail input, preventing the Heat Fail diagnostic.

The ignition electrode (4E1) will spark continuously for 4.7 seconds in an attempt to establish a flame. The flame is proven by the flame rod (4U19). The system will operate in the low heat mode until there is an additional call for heat established by closing the K1 contacts on the Heat Mod- ule.

The 60 second sequencing time delay relay (4DL6) will energize the combustion blower relay (4K33) which switches the combustion blower motor to high speed and energizes the 2nd stage solenoid on the gas valve (4L15).

Unit Start-Up (Continued)

If the flame rod (4U19) does not detect a flame at the time of an initial call for heat or detects a loss of flame during operation, it will de-energize the gas valve and the inter- lock relay (4K32). The Fenwal ignition control board

(4U18) will lockout automatically. If a flame failure occurs prior to the sequencing time delay relay (4DL6) opening its contacts which de-energizes the pre-purge timer (4DL5), the sequencing time delay relay (4DL6) will complete its timing. When completed, the pre-purge time delay relay (4DL5) is de-energized, opening its contacts which discon- nects power to the ignition control board (4U18), the se- quencing time delay relay (4DL6), and the 2nd stage sole- noid on the gas valve (4L15). Once power is removed from the ignition control board, it will reset automatically. If a call for heat still exists, after approximately 60 seconds, the contacts for the sequencing time delay relay (4DL6) will close, powering the pre-purge time delay circuit while tim- ing open to the combustion blower relay (4K33) and the 2nd stage solenoid on the gas valve (4L15). The pre-purge time delay relay (4DL5) will initiate another ignition se- quence. The combustion blower motor will continue to op- erate as long as a heating requirement exists and the ser- vice switch (4S24) is "On".

Once the heating demand has been satisfied, the combus- tion blower motor and the ignition control board is de-ener- gized.

Propane Gas

Units that operate on propane gas have one additional con- trol that affects the combustion blower motor operation when a heating demand has been initiated or satisfied. The post purge time delay relay (4DL4) is installed which delays the starting of the combustion blower by approxi- mately 60 seconds. Once it has timed out, the combustion blower motor will start, closing the combustion air flow switch (4S25). The ignition sequence will follow the same sequence from the combustion airflow switch (4S25) to the subsequent controls as a natural gas system.

Once the heating demand has been satisfied, the Fenwal ignition control board (4U18) and the post purge time delay relay (4DL4) is de-energized. The combustion blower motor will continue to operate for approximately 15 seconds to purge the heat exchanger on the "Off" cycle.

Honeywell Ignition System

(500 & 850 MBH Natural Gas)

When a heating requirement exists, the Rooftop Module (RTM) starts the supply fan and sends a request for heat to the Heat Module. The Heat Module closes K1 contacts and starts the combustion blower motor (4B11). The combustion blower motor starts on low speed through the normally closed combustion blower relay (4K33) contacts.

The supply airflow switch (4S38) and the combustion air switch (4S25) closes. Power is applied through the high limit cutout (4S26) to the Honeywell ignition control board (4U18). The ignition control board (4U18) starts a pre-purge timing cycle. At the end of the pre-purge cycle, the ignition transformer (4T7) and the pilot solenoid valve (4L9) are en- ergized. This starts a 10 second trial for pilot ignition. When the pilot flame is established and sensed by the flame sens- ing rod (4U19), stage 1 of the main gas valve (4L7) and the 60 seconds sequencing time delay relay (4DL6) is ener- gized.

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Contents Later Design Sequence ModelsWith 3-DTMScroll Compressors Literature Change History Overview of ManualTable of Contents General Information Model Number DescriptionDigit 3 Unit Airflow General Information Commonly Used Acronyms Fiberglass WoolHazard Identification Unit DescriptionGeneral Information Supply AIRVentilation Control Module VCM Design special option only CFMLead-Lag Constant Volume CV Units Variable Air Volume VAV Units Unit Component Layout and Shipwith LocationsGeneral Information Space Temperature Averaging Control Module Locations for SHF 40, 60, 70 & 75 Ton Units Table of Contents Unit Inspection As soon as the unit arrives at the job site Unit Dimensions & Weight InformationNo Step Surface StoragePage Sahf Cooling-Only Units 20 thru 75 Ton Unit Base Dimensional Data Dimensions InstallationUnit Dimensional Data Dimensions Size Electrical Entrance Data Unit DimensionsSEHF, SFHF, SLHF, SSHF, Sxhf Units 20 thru 75 Ton Electrical Entrance Data Unit Dimensions Size Unit Base Dimensional Data Dimensions SizeUnit Dimensions Size Unit Size Furnace Dimensions Note Size/MBH Length HeightSHG Cooling & Heating Units 90 through 130 Ton Slhf SahfSehf SshfSE,SL Roof Curb and DuctworkSahf Sshf Sfhf Sxhf Sehg Sfhg Sxhg HF/G Heavy Objects Installation Unit Rigging & PlacementIf a Trane Curb Accessory Kit is not used Pitch Pocket LocationTypical Unit Rigging Unit Base & Roof Curb Section General Unit Requirements Main Electrical Power RequirementsInstallation Field Installed Control Wiring Requirements for Electric Heat UnitsInstallation Condensate Drain Connections Page Removing Supply and Exhaust Fan Shipping Channels Motors 5Hp Page Installation Sensor & Tubing Installation Units with StatitracTMHazardous Gases and Flammable Vapors Connecting the Gas Supply Line to the Furnace Gas TrainGas Heat Units SFH 350 MBH 850 MBH 1000 MBH Modulating 500 MBH 1000 MBH Flue Assembly InstallationFlue Assembly Hot Water Heat Units SLHSteam Heat Units SSH SSHG-90Through 130 Ton units Page Live Electrical Components Hazardous VoltageUse Copper Conductors Only Typical Field Power Wiring 20 thru 75 Ton Page Exhaust Fan Motor Supply Fan Motor FLA ea HorsepowerCondenser Fans Total FLA FLABlower Motor Sfhf Only CombustionUnit Tonnage No. of Compressors Tonnage Type Designation = Current of the Largest Motor Compressor or FAN Motor Single Source Power 380V, 415V, 460V,Load Definitions Load On the NextDual Source Power units 200V Power Wire Sizing and Protection Device EquationsDisconnect Switch Sizing DSS MCA = 1.25 x Load MOP = 1.25 x LoadInstallation Controls using DC Analog Input/Outputs Controls using 24 VACConstant Volume System Controls Variable Air Volume System Controls Constant Volume or Variable Air Volume System ControlsPressurize DepressurizePurge FireRefer to Wiring Notes on 16A16B Page 17A 17B VAV Setpoint Input VoltageTable of Contents Cooling Sequence of Operation Sequence of OperationUnit Start-Up Gas Heating Sequence of OperationFenwal Ignition System Propane GasFlame Failure Modulating Gas Sequence of OperationFull and Limited Modulating Gas Furnace Unit Start-Up Wet Heat Sequence of Operation Electric Heat Sequence of OperationFreeze Protection Compressor Damage Unit PowerElectrical Phasing Voltage Supply Voltage Supply and Voltage ImbalanceVoltage Imbalance Service Test Guide for Component Operation IGVSupply FAN Verifying Proper Fan Rotation System Airflow Measurements Constant Volume SystemsRotating Components If all of the fans are rotating backwardsCondenser Fan Location with Human Interface Designator Variable Air Volume Systems Optional with all Units Exhaust Airflow MeasurementTraqTM Sensor Airflow Measurement Optional with all units equipped with an economizer20 & 25 Ton Supply Fan Performance without Inlet Guide Vanes Ton Supply Fan Performance without Inlet Guide VanesWocfm 1200 RPM 40 HP 40% 300 RP Standard Evaporator Coil 20000 30000 40000 50000 60000 Drop 20 & 25 Ton Supply Fan Performance with Inlet Guide Vanes Ton Supply Fan Performance with Inlet Guide Vanes15 HP 900 RPM 80% 10 HP RPM Through 75 Ton Component Static Pressure Drops Inches W.C AIRAIR STDCFM RPM BHP 10,000 HF-C20 000HF-C25 000 HF-C30 000RPM BHP BHP RPM BHP RPM BHP AIR RPM BHPExhaust Air Dampers Economizer Damper AdjustmentTo Adjust the Fresh Air Damper Travel Fresh Air & Return Air Damper OperationConfiguration Damper Travel Adjustment PositionConnecting Rod Crank Arm Hole Ton UnitsAll Systems Fresh Air & Return Air Linkage AdjustmentCompressor Start-Up 70 & 105 TonAt Shutdown Compressor Operational SoundsRefrigerant Charging At Low Ambient Start-UpCompressor Locations Cooling Cycle Pressure Curve 340 320 Full Load 380 360 340 OD Ambient Full Load 380 360 340 OD Ambient 320 240 220 380 360 OD Ambient Charging by Subcooling Thermostatic Expansion ValvesLow Ambient Dampers Electric, Steam and Hot Water Start-Up Gas Furnace Start-UpLow-Fire Adjustment 500 MBH, 850 & 1,000 MBH only High-Fire AdjustmentCombustion Air Adjustment O2 Two Stage Gas FurnaceFiring Manifold MBHCO2 Pressure Heat Exchanger Full Modulating Gas FurnaceUnit control Modulating Gas Regulator Limited Modulating Gas Furnace Unit Start-UpModulating Gas Regulator Legend Unit Start-Up Final Unit Checkout Typical Gas FurnaceService & Maintenance Service & Maintenance Unit Internal Fuse Replacement Data & VFD Factory SettingsWet Heat Coil Fin Data Total Coil Fins Unit Model Box-type Note QtyQty Size of each Model TypeService & Maintenance Fan Belt Adjustment Suction Line Filter/Drier Installation Scroll Compressor ReplacementGripbelts Gripnotch Cross Small P.D Section Range Min Max VFD Programming Parameters Hazardous Voltage! w/CapacitorsSupply and Exhaust Fan VFD Programming Parameters Filters Service & Maintenance Monthly MaintenanceCooling Season Coil Cleaning Heating SeasonContains Refrigerant Coil CleanersSteam or Hot Water Coils Final Process Index See Figure Gate type valve 36-37 See -12 Figure See VOM Contacts -16 Figure Warranty and Liability Clause Equipment Damage From Ultraviolet UV Lights115 116
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