Bryant 120 instruction manual Two-Stage Heating Adaptive mode with Single-Stage Thermostat

Page 52

312A

control CPU, transformer TRAN, inducer motor IDM, blower motor BLWM, hot-surface igniter HSI, and gas valve GV.

1.Two-Stage Heating (Adaptive mode) with Single-Stage Thermostat

(See Fig. 24 or 33 for thermostat connections)

NOTE: The low-heat only switch (LHT) selects either the low-heat only operation mode when ON, (see item 2. below) or the adaptive heating mode when OFF in response to a call for heat. (See Fig. 34.) When the W2 thermostat terminal is energized it will always cause high-heat operation when the R to W circuit is closed, regardless of the setting of the low-heat only switch. This furnace can operate as a two-stage furnace with a single-stage thermostat because the furnace control CPU includes a programmed adaptive sequence of controlled operation, which selects low-heat or high-heat operation. This selection is based upon the stored history of the length of previous gas-heating periods of the single-stage thermostat.

The furnace will start up in either low- or high-heat. If the furnace starts up in low-heat, the control CPU determines the low-heat on-time (from 0 to 16 minutes) which is permitted before switching to high-heat.

If the power is interrupted, the stored history is erased and the control CPU will select low-heat for up to 16 minutes and then switch to high-heat, as long as the thermostat continues to call for heat. Subsequent selection is based on stored history of the thermostat cycle times.

The wall thermostat “calls for heat”, closing the R to W circuit. The furnace control performs a self-check, verifies the low-heat and high-heat pressure switch contacts LPS and HPS are open, and starts the inducer motor IDM in high-speed.

a. Inducer Prepurge Period

(1.) If the furnace control CPU selects low-heat operation the inducer motor IDM comes up to speed, the low-heat pressure switch LPS closes, and the furnace control CPU begins a 15-second prepurge period. After the low-heat pressure switch re-closes the furnace control CPU will begin a 15-second prepurge period, and continue to run the inducer motor IDM at high-speed.

(2.) If the furnace control CPU selects high-heat operation, the inducer motor IDM remains running at high-speed, and the high-heat pressure switch relay HPSR is de-energized to close the NC contact. When sufficient pressure is available the high-heat pressure switch HPS closes, and the high-heat gas valve solenoid GV-HI is energized. The furnace control CPU begins a 15-second prepurge period after the low-heat pressure switch LPS closes. If the high-heat pressure switch HPS fails to close and the low-heat pressure switch LPS closes, the furnace will operate at low-heat gas flow rate until the high-heat pressure switch closes for a maximum of 2 minutes after ignition.

b.Igniter Warm-Up-At the end of the prepurge period, the (Hot Surface Igniter) HSI is energized for a 17-second igniter warm-up period.

c.Trial-for-Ignition Sequence-When the igniter warm-up period is completed the main gas valve relay contacts GVR-1 and -2 close to energize the gas valve solenoid GV-M, the gas valve opens, and 24 vac power is supplied for a field-installed humidifier at the HUM terminal. The gas valve solenoid GV-M permits gas flow to the burners where it is ignited by the HSI. Five sec after the GVR closes, a 2-sec flame proving period begins. The HSI igniter will remain energized until the flame is sensed or until the 2-sec flame proving period begins. If

the furnace control CPU selects high-heat operation, the high-heat gas valve solenoid GV-HI is also energized.

d.Flame-Proving-When the burner flame is proved at the flame-proving sensor electrode FSE, the inducer motor IDM switches to low-speed unless running at high-speed, and the furnace control CPU begins the blower-ON delay period and continues to hold the gas valve GV-M open. If the burner flame is not proved within two seconds, the control CPU will close the gas valve GV-M, and the control CPU will repeat the ignition sequence for up to three more Trials-For-Ignition before going to Ignition- Lockout. Lockout will be reset automatically after three hours, by momentarily interrupting 115 vac power to the furnace, or by interrupting 24 vac power at SEC1 or SEC2 to the furnace control CPU (not at W/W1, G, R, etc.). If flame is proved when flame should not be present, the furnace control CPU will lock out of Gas-Heating mode and operate the inducer motor IDM on high speed until flame is no longer proved.

e.Blower-ONDelay-If the burner flame is proven the blower-ON delay for low-heat and high-heat are as follows:

Low-Heat-45 seconds after the gas valve GV-M is energized the blower motor (BLWM) is energized at LO HEAT speed.

High-Heat-25 seconds after the gas valve GV-M is energized the BLWM is energized at HI HEAT speed. Simultaneously, the electronic air cleaner (EAC-1) terminal is energized and remains energized as long as the BLWM is energized.

f.Switching from Low-to High-Heat-If the furnace control CPU switches from low-heat to high-heat, the furnace control CPU will switch the inducer motor IDM speed from low to high. The high-heat pressure switch relay HPSR is de-energized to close the NC contact. When sufficient pressure is available the high-heat pressure switch HPS closes, and the high-heat gas valve solenoid GV-HI is energized. The blower motor BLWM will switch to HI HEAT speed five seconds after the furnace control CPU switches from low-heat to high-heat.

g.Switching from High- to Low-Heat-The furnace control CPU will not switch from high-heat to low-heat while the thermostat R-to-W circuit is closed when using a singlestage thermostat.

h.Blower-OFF Delay-When the thermostat is satisfied, the R to W circuit is opened, de-energizing the gas valve GV-M, stopping gas flow to the burners, and de-energizing the humidifier terminal HUM. The inducer motor IDM will remain energized for a 5-second post-purge period. The blower motor BLWM and air cleaner terminal EAC-1 will remain energized for 90, 120, 150, or 180 seconds (depending on selection at blower-OFF delay switches). The furnace control CPU is factory-set for a 120-second blower-OFF delay.

2.Two-Stage Thermostat and Two-Stage Heating (See Fig. 32 for thermostat connections)

NOTE: In this mode the LHT must be ON to select the low-heat only operation mode in response to closing the thermostat R-to-W1 circuit. Closing the thermostat R-to-W1-and-W2 circuits always causes high-heat operation, regardless of the setting of the low-heat-only switch.

The wall thermostat “calls for heat”, closing the R-to-W1 circuit for low-heat or closing the R-to-W1 and-W2 circuits for high-heat. The furnace control performs a self-check, verifies the

52

Page 51 Page 53
Image 52
Page 51 Page 53
Contents Ama Furnace Reliability Hazard Safety ConsiderationsCUT Hazard Dimensions IntroductionWidth Bottom Flue Cabinet SizeInstallation Electrostatic Discharge ESD Precautions Procedure Codes and StandardsGeneral LocationCarbon Monoxide Poisoning and Unit Damage Hazard FIRE, Injury or Death Hazard Fire HazardProperty Damage Hazard Location Relative to Cooling EquipmentAIR for Combustion Ventilation Furnace Corrosion HazardCarbon Monoxide Poisoning Hazard Outdoor Combustion Air MethodAir for Combustion, Ventilation and Dilution for Outdoors Installation Upflow InstallationDownflow Installation Horizontal InstallationFIRE, EXPLOSION, and Carbon Monoxide Poisoning Hazard Suspended Furnace SupportFloor and Plenum Opening Dimensions Roll-Out ProtectionFurnace Plenum Opening Floor Opening Casing Opening dimensionsWidth Horizontal Unit Suspension Filter Arrangement Carbon Monoxide Poisoning Hazard AIR DuctsGeneral Requirements Ductwork Acoustical Treatment Supply Air ConnectionsAir Delivery CFM With Filter Speed External Static Pressure IN. WC Size Inlet2380 2285 2200 2085 1970 1835 Air Delivery CFM With Filter* Downflow FurnacesReturn Air Connections GAS Piping Fire or Explosion HazardUpflow Return Air Configurations and Restrictions Maximum Capacity of Pipe Furnace Damage HazardWiring Electrical Connections Electrical Shock and Fire HazardElectrical Shock Hazard Furnace MAY not Operate HazardBOX Relocation Electrical DataElectrical Connection to J-BOX Power Cord Installation in Furnace J-BOX BX. Cable Installation in Furnace J-BOXElectrical Box on Furnace Casing Side. See Fig Fire or Electrical Shock HazardTwo-Stage Furnace with Two-Speed Air Conditioner See notes 2, 11, and 12 on the page following these figures Accessories VentingGeneral Venting Requirements Masonry Chimney RequirementsChimney Inspection Chart Appliance Application Requirements Vent Height Internal Area of ChimneyUpflow Application-Vent Elbow Up Downflow Application-Vent Elbow Up Horizontal Right Application Vent Elbow Right Furnace Vent Orienta Orientation Tion PUTBTUH/HR Diameter Height FTRounded End of Knockout Burn HazardSTART-UP, ADJUSTMENT, and Safety Check Start-Up ProceduresGeneral Fire and Explosion HazardAdjustments Stage Furnace Setup Switch DescriptionU.S Altitude Derate Multiplier for U.S.ARedundant Automatic Gas Control Valve Furnace Overheating Hazard Gas Rate cu ft/hrSeconds Size of Test Dial For Revolution Speed Selection Color Speed AS ShippedStage Furnace Blower OFF delay Setup Switch Check Safety ControlsDesired Heating Mode Setup Switch Blower OFF Delay SEC Checklist Altitude Range Specific Gravity of Natural GASBTUH/CU Gravity6001 to BTUH/CU FT Specific Gravity of Natural GAS Altitude RangeSpecific Gravity of Natural GAS Altitude Range Heat Value Service and Maintenance Procedures Electrical SHOCK, Fire or Explosion HazardFIRE, Personal Injury and Unit Damage Specific Gravity of Natural GAS Heat Value AT AltitudeCare and Maintenance Electrical Controls and Wiring Electrical Shock HazardIntroduction Unit Operation HazardService Wiring Diagram Cleaning AND/OR Replacing AIR Filter Filter size informationBlower Motor and Wheel Electrical Shock Hazard Furnace Filter Size CasingCleaning Heat Exchanger Unit Damage HazardSequence of Operation Igniter Position Top ViewTwo-Stage Heating Adaptive mode with Single-Stage Thermostat Thermidistat Mode Single-Stage Thermostat and Two-Speed Cooling Adaptive ModeSingle-Speed Cooling Troubleshooting Wiring DiagramsContinuous Blower Mode Troubleshooting Guide 2-Speed Blocked vent shutoff switch used in Chimney Adapter Kit Page Catalog No. II312A---45---8

120 specifications

The Bryant 120 is a remarkable system designed for residential and commercial heating and cooling needs, showcasing an impressive blend of efficiency, reliability, and advanced technology. As a part of Bryant's extensive line of HVAC solutions, the Bryant 120 stands out with its features and performance, making it an ideal choice for those seeking comfort year-round.

One of the main features of the Bryant 120 is its exceptional energy efficiency. It boasts a high Seasonal Energy Efficiency Ratio (SEER) rating, enabling homeowners to save on energy costs while enjoying consistent temperature control. This efficiency is aided by its variable-speed compressor, which allows the system to adjust its output based on current requirements, optimizing both energy consumption and comfort.

In terms of technology, the Bryant 120 incorporates advanced controls that enhance user experience and system performance. The system comes equipped with smart thermostats that allow homeowners to monitor and adjust their environment remotely. These thermostats not only provide convenience but also help in optimizing energy usage by learning the household's heating and cooling patterns.

Another characteristic of the Bryant 120 is its durable construction. The unit is built to withstand various weather conditions, featuring a robust cabinet and components designed for longevity. This durability ensures that homeowners can rely on the system for years without the need for frequent repairs or replacements.

Noise levels are also a critical consideration in HVAC systems, and the Bryant 120 addresses this with its quiet operation. The system is designed to minimize sound output, making it suitable for residential areas where noise can be a concern. This is particularly beneficial for nighttime use, providing a comfortable sleeping environment.

Additionally, the Bryant 120 supports eco-friendly refrigerants that comply with environmental standards, contributing to a reduction in greenhouse gas emissions. This commitment to sustainability reflects Bryant's dedication to creating products that are not only effective but also responsible.

Overall, the Bryant 120 encapsulates a harmonious balance of efficiency, advanced technology, durability, and quiet operation. Whether for a new installation or a replacement, the Bryant 120 presents an ideal solution to meet diverse heating and cooling requirements, enhancing comfort while prioritizing energy savings and environmental responsibility.
Top Page Image Contents