FieldBench
Models
Bryantfurnace

820S

Preferred 80 · single-stage · variable-speed · Cat I

Bryant Preferred 80% single-stage VS (821S Low-NOx). Metal vent. One PS. VS blower like 926S — Category I physics like 800S. Not 820T two-stage.

Not 820T two-stage. Not 800S Legacy 18-speed. Not 926S (96% PVC).

Diagnose this modelInstall notesBoard cross-refField wiring

AFUE

80% single-stage · Cat I

Blower

Preferred VS

Sister SKU

821S Low-NOx · Carrier 58SP0 / 58SP1

This board

Two-digit IFC · 80% single-stage

  • 11–14, 21–24, 31, 33, 34. Same Comfort 80 language as Carrier 58STA.
  • No 58/59 condensate pair. If you see those numbers you are on a 96% or a Rheem.
  • 820S adds VS / InteliSense — 41/44 can appear. 31 is still metal-vent draft.

Write the two-digit code before a power cycle.

Universal swap

No universal

Preferred 80% VS single-stage. Not a 50A55 80% PSC drop-in.

White-Rodgers

—

ICM

—

Honeywell

—
  • 50A55-843 ‘because 80%’. 800S Legacy board assumed.

After you pull the dead card

  1. 1OEM Preferred 80% VS IFC. Metal vent.

Field wiring

Written landings for Bryant 820S. Not a factory schematic.

Furnace · single-stage 24V
R / C / W / Y / GGas furnace

Conventional single-stage furnace IFC. One W. Cool Y passes through to the outdoor. No ComfortBridge, no ABCD, no W2.

Written circuit description only — FieldBench does not redraw maker schematics. Example: R to W closes on a heat call; verify 24V at W1 before you change the IFC.

Open manufacturer PDF

Heat sequence

  1. 1Power. L1 / N → IFC → transformer → R120V in, 24V out
  2. 2Call. Stat W → IFC W~24 VAC
  3. 3Draft. IFC → inducer → PS close120V motor, 24V prove
  4. 4Ignite. IFC → HSI120 VAC
  5. 5Gas. IFC → valve~24 VAC
  6. 6Flame. Rod → IFCµA DC
  7. 7Blow. IFC → heat speedAfter flame prove

This indoor

Preferred 80% single-stage VS. One W.

24V single-stage heat

Door card is one-stage. Twin terminal empty unless the job is actually twinned.

Wall thermostat

Single-stage heat/cool. W2 from a leftover two-stage stat does nothing useful.

  • R24V hot from the IFC24V
  • CCommon24V
  • WHeat24V
  • YCool — also starts the outdoor24V
  • GFan24V

Furnace IFC

Transformer lives here. Y out to the outdoor contactor. TWIN empty on a standalone.

  • RHot to the stat24V
  • CCommon — must reach the outdoor24V
  • WHeat call24V
  • YCool in / cool out24V
  • GBlower24V
  • TWINEmpty unless twinned24V

Landing

  • 24VIFC Rstat R

    ~24 VAC hot

  • 24VIFC Cstat Coutdoor C

    Common

  • 24VStat WIFC W

    Heat. Stays in this cabinet.

  • 24VStat YIFC Youtdoor Y

    Cool / contactor

  • 24VStat GIFC G

    Fan. Does not go outdoors.

IFC harness — single-stage heat

After W arrives. This is the gas train, not the thermostat strip.

Transformer + fuse

120V primary. 24V secondary. Dark stat = fuse / door / transformer first.

  • L1 / N120V to the IFCLine
  • XFMR24V to R24V
  • FUSEOn the IFC24V

24V safety chain

Door, limit, rollout in series. Open anywhere kills heat.

  • DOORInterlock24V
  • LIMITMain limit — rise / no airflow24V
  • ROLLOUTManual reset. Do not jumper and leave24V

Inducer + one pressure switch

W → inducer 120V → PS closes → IFC continues. One hose, one switch.

  • IND120V from the IFC to the inducerLine
  • PS24V prove back to the IFC24V
  • HOSESingle hose. Do not add a second because two-stage boards have two.24V

HSI + single valve

Igniter is 120V from the IFC. Valve is 24V. Flame rod is µA DC back to the IFC.

  • HSI120V hot-surface igniter — not 24VLine
  • VALVE24V to the single solenoid24V
  • FLAMEµA DC on the rod. Not a 24V circuit24V

PSC blower + run cap

Heat / cool / park taps on the motor. The cap is on this blower — not the outdoor dual can.

  • HEATHeat speed tap24V
  • COOLCool speed tap24V
  • PARKUnused leads parked24V
  • CAPRun capacitor on the blowerCap

Landing

  • LineL1IFCinducer

    120 VAC after W

  • 24VIFCPSIFC

    ~24 VAC prove. Open PS = no ignition.

  • LineIFCHSI

    120 VAC during trial

  • 24VIFCgas valve

    ~24 VAC after flame prove starts

  • 24VFlame rodIFC

    µA DC. Not 24V.

  • LineIFCblower

    120V tap + cap

Prove it

  • 24 VAC from R to C at the IFC. Fuse / transformer first if the stat is dark.
  • W at the IFC under a heat call. Then inducer / igniter / valve per THIS door card.

Do not

  • Do not land a ComfortBridge 1/2 or Infinity ABCD pair on this IFC.
  • Do not hunt W2 / E8 / high-fire on a one-stage door.
  • TWIN must be empty on a standalone.

9-speed tap, PSC, and CT motors share this thermostat landing. The motor is on the IFC harness diagram.

Sequence

  1. 1

    W

    Inducer → metal-vent prove → HSI → valve → flame → blower. Chimney and common vent matter.

Faults on this IFC

Step 1, then 2, then 3. Expected reading and the fail branch sit under each check.

13 / 33

Limit

warn

Airflow. 80% coil on top is still a dirty A-coil.

  1. 1 Airflow before you touch the limit

    On Bryant 820S a limit is airflow or overfire until proven otherwise. Do not replace the limit first. Filter, blower wheel, A-coil, and the heat-speed setting for THIS motor (tap, model plug, or communicating CFM — not a sister SKU chart). Filter, heat speed / VS setup, coil.

    Expect: Rise in the rating-plate window. Static vs this cabinet’s blower chart.

  2. 2 Measure static and temperature rise

    Total external static vs the Bryant 820S blower chart for this cabinet size. Supply minus return rise after 8–10 minutes. A new 5" media cabinet or closed supplies will trip this all winter.

    Expect: Rise typically 35–65 °F — rating plate wins.

    If fail: Fix the restriction or the heat-speed setting. The limit is doing its job.

    If pass: Airflow in range → step 3 (overfire / limit itself).

  3. 3 Overfire, then the limit circuit

    Clock the meter / manifold on the stage that is tripping vs the rating plate. Then ohm the limit after it cools — a limit that never recloses is failed. Rollout in the same circuit is a different call (see rollout on this door card).

    Expect: Manifold on plate. Limit closed when cool.

14 / 34

Ignition

lockout

HSI / gas / rod.

  1. 1 Ohms at the igniter, then at the IFC

    On Bryant 820S measure cold ohms at the igniter plug, then at the IFC connector. An open at the plug is the element or local harness. Open only at the IFC is the harness rub-through on the collector. Fix 31 draft before a fair 34 test.

    Expect: Nitride cold ohms per THIS door sticker — do not use an 80% Norton chart.

  2. 2 120 VAC during warm-up

    Call for heat and measure 120 VAC at the igniter during the warm-up window. 0 V + good ohms = IFC igniter relay. Voltage + no glow = cracked nitride.

    Expect: 120 VAC only during warm-up. Visible glow before the valve opens.

  3. 3 Do not keep cycling a cracked element

    A cracked nitride can ohm ‘good’ cold and open hot. If ohms and voltage are good and there is no glow, replace the igniter. Confirm polarity/ground (this plate’s polarity code) before you condemn a new igniter.

    Expect: One clean light after a known-good igniter and a proven ground.

31

Draft / PS

lockout

Metal vent will not prove.

  1. 1 Prove inducer and the live code

    Do not pull power — that clears the Bryant 820S active code. Write 31. Is the inducer spinning on this call? Silent inducer is not a pressure switch. This is Category I metal vent. There is no 96% collector or PVC trap to prime.

    Expect: 120 VAC at the inducer on a heat call. Wheel turning.

    If fail: 120 VAC missing → IFC / door switch / incoming power. Voltage + dead motor → inducer.

    If pass: Inducer running + this code → trap, hose, switch, vent (step 2).

  2. 2 Trap, collector, and the hose

    A drowned 96% trap will not make collector pressure. Pull the trap, flush it, confirm the collector box and inducer outlet are not full. Hose cracked, off the port, or full of water fakes an open switch. Cap, liner, common-vent tables, inducer wheel, hose on the inducer housing.

    Expect: Trap flowing, hose dry and downhill, ports not swapped on a two-switch board.

  3. 3 Switch ohms, then vent load

    Ohm the pressure switch: NO, must close when that inducer speed is making the collector setpoint. If the switch is good, walk the PVC — bird screen, ice, long 2" run, wind, shared chase. Cap, liner, common vent, inducer wheel. Not a PVC trap.

    Expect: Switch closes on known draft. Vent unrestricted.

    If fail: Replace the open switch only after the vent and trap are proven.

    If pass: Switch closes on draft and the code stays → IFC input.

41 / 44

Blower (820S VS)

lockout

Preferred VS 80% only.

  1. 1 Is the wheel free?

    Spin the Bryant 820S blower by hand. Ice, debris, or a seized bearing is not a control problem. Confirm the motor type on this plate — serial ECM, 9-speed tap, or X-13 — before you grab a capacitor. If this is an 800S 18-speed, 41 is the wrong card — confirm the plate.

    Expect: Wheel free. Correct motor family for this IFC.

  2. 2 Command vs rotation

    Call for G or heat and confirm the IFC is actually requesting CFM (taps, serial, or communicating). Amp the motor. Locked rotor + a good command = motor. No command = IFC / harness / shared data.

    Expect: Command present. Motor amps in range, not locked.

  3. 3 Static and the wrong motor

    High static will trip current/limit codes and look like a dead motor. Measure TES vs this cabinet. Wrong horsepower or a leftover memory card after a control swap is the other half of this call.

    Expect: Static on the blower chart. Matching motor / shared-data card.

Workflows

31 on 820S

Inducer on, no light.

  1. 1 Prove the call and the live code

    One draft switch. Metal vent. Cap / liner / common vent.

    Expect: Write whatever Two-digit IFC · 80% single-stage is showing. Write the two-digit code before a power cycle.

    If fail: No call at the IFC → stat / harness. Do not change gas parts.

  2. 2 Isolate the first failed step in the sequence

    VS heat CFM / setup — not an 800S tap.

    Expect: The first dead output or open prove.

  3. 3 Confirm with a number, then the next part

    VS heat CFM / setup — not an 800S tap.

    Expect: Vent: Cat I. Spillage is a fail.

    If fail: Stay on this plate. The out-of-range reading is the part.

    If pass: Reading in range → the next step in this workflow is the repair.

Test points

Vent

Cat I. Spillage is a fail.

Gotchas

  • 800S is Legacy 18-speed Comfort 80. This is Preferred VS.

Related plates

Install this plate

Install Bryant 820S as Preferred 80 · single-stage · variable-speed · Cat I.

Preferred 80 · single-stage · variable-speed · Cat I

This plate — not the sister SKU

  • Not 820T two-stage. Not 800S Legacy 18-speed. Not 926S (96% PVC).
  • 800S is Legacy 18-speed Comfort 80. This is Preferred VS.

IFC on this door

  • 11–14, 21–24, 31, 33, 34. Same Comfort 80 language as Carrier 58STA.
  • No 58/59 condensate pair. If you see those numbers you are on a 96% or a Rheem.
  • 820S adds VS / InteliSense — 41/44 can appear. 31 is still metal-vent draft.

Hardware

  • AFUE: 80% single-stage · Cat I
  • Blower: Preferred VS
  • Sister SKU: 821S Low-NOx · Carrier 58SP0 / 58SP1

First fire

  1. 1One draft switch. Metal vent. Cap / liner / common vent.
  2. 2VS heat CFM / setup — not an 800S tap.

Do not on Bryant 820S

  • Not 820T two-stage. Not 800S Legacy 18-speed. Not 926S (96% PVC).
  • 800S is Legacy 18-speed Comfort 80. This is Preferred VS.

Maker literature

FieldBench does not host manufacturer files. Each link opens the maker’s own literature page in a new tab.

  • Bryant document searchLiterature searchEnter the full Bryant plate (926TB60100V21, 987MA…). Owner PDFs are public; many I/Os are dealer-gated.Open manufacturer PDF
  • Bryant document searchLiterature searchSearch Bryant 820S on the maker’s literature page.Open manufacturer PDF

Warranty and bulletins

Affected models, serial range, symptom, remedy, date. Maker files open on the manufacturer site.

All bulletins

  • Residential limited warranty

    warranty sheet

    Carrier / Bryant registered heat-exchanger terms

    Current 59-series / Evolution / Preferred registered warranty · Limited warranty certificate

    Open factsOpen manufacturer PDF

  • Dealer portals

    dealer

    Where remaining service letters live

    Current-year service letters not on a public literature page · Maker dealer portal

    Open factsOpen manufacturer PDF