FieldBench
Models
Bryantfurnace

987T

Evolution · two-stage · communicating · 97%

Bryant Evolution two-stage 97%. Twin of Carrier 59TN7. Discrete 31/32, ABCD bus. Not 987M modulating and not 986T (previous Evolution two-stage).

Not 987M modulating. Not 986T previous two-stage Evolution. Not 927T Preferred 24V.

Diagnose this modelInstall notesBoard cross-refField wiring

AFUE

Up to 96.7–97% Evolution two-stage

Sister SKU

Carrier 59TN7

This board

Evolution IFC + two-digit codes (two-stage, not modulating)

  • Evolution wall control Last 10 first. Board two-digit still flashes 24, 31, 32, 33, 13, 34, 14, 41.
  • 31/32 are discrete low vs high pressure switches — opposite of 987M, where 31/42 is a band.
  • ABCD polarity, one Evolution control, C required. Do not land a 24V Preferred stat on ABCD.

Evolution events first. Board last-status if the stat is dead.

Universal swap

No universal

Evolution two-stage. No universal.

Silk: Evolution

White-Rodgers

—

ICM

—

Honeywell

—
  • Any 50A55-843 / 50A65-843 / 50M56U-843 / 50M56X-843 / S9200U1000 universal — those are conventional 24V HSI, not this data bus.
  • ICM280 / 2811 / 2810 / 282B — wrong IFC family.
  • 927T Preferred. 987M modulating card.

After you pull the dead card

  1. 1OEM Evolution two-stage IFC. Pair the ABCD bus.

Field wiring

Written landings for Bryant 987T. Not a factory schematic.

Infinity / Evolution furnace
ABCDGas furnace

59MN7 / 59TN6 / 987M / 986T class. Four-wire communicating furnace. D is 24V hot, not W and not Y.

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 → IFC120V
  2. 2Call. Data pair or 24V W → IFCBus or 24V
  3. 3Draft. IFC → inducer → proveTwo-stage PS or a pressure band
  4. 4Ignite. IFC → HSI → valve120V igniter
  5. 5Blow. IFC → serial ECMNo tap, no cap

This indoor

Current Evolution two-stage.

ABCD only

Infinity or Evolution wall control and a matching outdoor.

Infinity / Evolution control

A/B data, C common, D 24V hot.

  • ADataData
  • BDataData
  • C24V common24V
  • D24V hot — not W24V

Infinity / Evolution IFC

Same ABCD. Do not convert it to 24V by landing W and walking away.

  • ADataData
  • BDataData
  • CCommon24V
  • D24V hot24V

Landing

  • DataStat A/BIFC A/Boutdoor A/B

    Data

  • 24VStat C/DIFC C/D

    24V common / hot. D is not Y or W.

IFC harness — communicating two-stage

Call arrives on the data pair (or 24V W). Gas train is still inducer / prove / igniter / valve.

Transformer + fuse

24V still exists for accessories and for a 24V outdoor. Data pair is not the transformer.

  • L1 / N120VLine
  • R / C24V strip24V
  • FUSEOn the IFC24V

24V safety chain

Limit / rollout / door still open the heat path. Codes are on THIS IFC language.

  • DOORInterlock24V
  • LIMITMain limit24V
  • ROLLOUTManual reset24V

Two-speed inducer + dual PS

Low vs high prove. Do not tee the hoses. Do not apply this to a modulating cousin.

  • IND LO/HITwo-speed inducerLine
  • LPSLow prove24V
  • HPSHigh prove24V

HSI + two-stage valve

Two solenoids or a two-stage valve. Staging is the bus or W1/W2, not a tap.

  • HSI120V igniterLine
  • MV / HV24V low / high solenoids24V
  • FLAMEµA DC24V

Serial variable-speed ECM

IFC talks to the motor on the serial harness. No F-taps. No dual run cap on this blower.

  • SERIALIFC-to-motor harness. Unplugged motor = CFM / comm fault, not a tap problem24V
  • CFMSet in the IFC menu / model plug / CoolCloud — not a dip switch on most of these24V

Landing

  • LineCallIFCinducerprove

    Low then high

  • LineIFCHSIvalve

    120V igniter, 24V or serial valve

  • 24VFlame rodIFC

    µA DC

  • DataIFCserial blower

    No F-taps. No PSC cap.

Prove it

  • Wall-control equipment list. The furnace and outdoor both present.
  • ABCD polarity. C still required.

Do not

  • Do not land W on a spare screw to make it 24V.
  • A 926T / 59TP6 / 59SC5 is the other diagram.

ABCD is the published Infinity / Evolution control.

Sequence

  1. 1

    Call

    Wall control requests a stage over ABCD. Valve is still two-stage (low then high).

  2. 2

    Low prove

    Low inducer → low PS (32). Same physics as 926T, different bus.

  3. 3

    High prove

    High inducer → high PS (31 on the high call). Second solenoid.

Faults on this IFC

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

24

Fuse

warn

24 V fuse.

  1. 1 Find the 24 V short before you replace the fuse

    On Bryant 987T an open IFC fuse is a short on W, Y, G, HUM, EAC, or a data pair landed on 24 V. Unplug the thermostat / data harness first. ABCD miswire, HUM/EAC, valve harness.

    Expect: Fuse out. 24 V transformer still good. Harness isolated.

  2. 2 Replace the fuse with the harness off

    New fuse, harness still off. If it holds, the short is in the field wiring or accessory. Plug one circuit back at a time (W, then Y, then HUM/EAC).

    Expect: Fuse holds with harness off. Dies when the shorted lead lands.

  3. 3 If it blows with the harness off

    Short is on the Bryant 987T IFC or the gas-valve harness. Unplug the valve and try once more. Repeat blow with valve unplugged = IFC.

    Expect: Do not keep feeding fuses into a welded valve coil or a burned IFC trace.

31

High / active-stage PS

lockout

High-fire or active-stage prove failed.

  1. 1 Prove inducer and the live code

    Do not pull power — that clears the Bryant 987T active code. Write 31. Is the inducer spinning on this call? Silent inducer is not a pressure switch. Does the inducer actually go high?

    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. High-fire hose not teed to the low switch.

    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. Vent capacity on 100/120 cabinets.

    Expect: LPS / HPS: Two NO switches. 32 vs 31. Never teed.

    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.

32

Low-fire PS

lockout

Low-stage draft not proven.

  1. 1 Prove inducer and the live code

    Do not pull power — that clears the Bryant 987T active code. Write 32. Is the inducer spinning on this call? Silent inducer is not a pressure switch. Trap, collector, low hose, attic PVC.

    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. Fix 32 before you chase 34.

    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.

    Expect: LPS / HPS: Two NO switches. 32 vs 31. Never teed.

    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.

33 / 13

Limit

warn

Airflow or rollout.

  1. 1 Treat this as flame outside the exchanger

    Do not reset the Bryant 987T rollout and walk away. Write the code, kill the call, and look for flame at the burners, crossover, and vestibule before you do anything else.

    Expect: No flame outside the exchanger. Burners seated. Crossover lit.

    If pass: Still inspect secondary / flue / condensate before you reset.

  2. 2 Secondary, condensate, and flue

    Blocked secondary, drowned collector, or a plugged flue pushes flame out the front. Pull the inducer/collector look, confirm the trap is flowing, and check PVC/vent. Evolution heat CFM, filter, coil. Rollout manual reset.

    Expect: Dry collector, open flue, trap clear.

  3. 3 Reset only after the cause is fixed

    Manual-reset rollout. Recurring rollout on Bryant 987T is a CO / fire call — cracked primary, misaligned burners, or a failed secondary. Confirm CO in the space before you leave.

    Expect: One clean cycle after the cause is fixed. No second reset as a repair.

34 / 14

Ignition

lockout

No flame prove.

  1. 1 Watch one full try — do not reset

    Write the Bryant 987T code. Watch inducer, HSI glow, valve click, flame, µA. The step that dies is the repair. Resetting only burns another try into a harder lockout. HSI, gas, rod. Fix 32 first if both store.

    Expect: Call → Low prove → High prove

  2. 2 Gas and the valve

    Cock open, inlet pressure, then manifold on the stage that is failing vs the rating plate. 24 VAC at the valve during trial? Coil ohms? A valve that never opens looks like a ‘bad igniter’ if you did not watch the sequence.

    Expect: Inlet and manifold on the plate. 24 VAC only during trial.

  3. 3 Flame prove, then the lockout timer

    Glow + valve + no prove → rod, ground, or IFC sense. Prove then drop → µA / PS / limit. Soft lockouts on this family often auto-reset on a long clock — do not sit on resets.

    Expect: Stable µA after light-off. No new PS/limit code.

ABCD

Communication

lockout

Wall control or outdoor dropped.

  1. 1 Data pair, not 24 V

    On Bryant 987T indoor/outdoor comm is a data pair (AB, S1/S2, U, ComfortBridge, ComfortLink — whatever THIS plate uses). It is not a 24 V Y. Check polarity, continuity, and that nobody landed it on R/C. A/B/C/D, polarity, C, one master.

    Expect: Pair continuous, not shorted to chassis, polarity per the diagram.

  2. 2 Power both ends, then the outdoor status

    Indoor transformer and outdoor control both alive. Read the outdoor LED / 7-seg. Water in the outdoor control is the usual dead-end after a storm.

    Expect: Both controls powered. Outdoor showing a comm or address state, not a blank board.

  3. 3 Address / bias, then the control

    Communicating plates need a matching indoor address and sometimes a terminating bias. Swap is last: known-good pair + power both ends + correct address.

    Expect: Indoor sees the outdoor. No comm code after a power cycle.

Workflows

987T vs 987M vs 986T

Evolution condensing.

  1. 1 Prove the call and the live code

    987M = modulating, pressure band. 987T / 986T = two-stage, discrete 31/32.

    Expect: Write whatever Evolution IFC + two-digit codes (two-stage, not modulating) is showing. Evolution events first. Board last-status if the stat is dead.

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

  2. 2 Isolate the first failed step in the sequence

    987T is the current two-stage Evolution. 986T is the previous plate.

    Expect: Low prove: Low inducer → low PS (32). Same physics as 926T, different bus.

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

    987T is the current two-stage Evolution. 986T is the previous plate.

    Expect: ABCD: Evolution pair. D is not W. · LPS / HPS: Two NO switches. 32 vs 31. Never teed.

    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

ABCD

Evolution pair. D is not W.

LPS / HPS

Two NO switches. 32 vs 31. Never teed.

Gotchas

  • 986T stays in the bench as the previous Evolution two-stage.

Related plates

Install this plate

Install Bryant 987T as Evolution · two-stage · communicating · 97%.

Evolution · two-stage · communicating · 97%

This plate — not the sister SKU

  • Not 987M modulating. Not 986T previous two-stage Evolution. Not 927T Preferred 24V.
  • 986T stays in the bench as the previous Evolution two-stage.

IFC on this door

  • Evolution wall control Last 10 first. Board two-digit still flashes 24, 31, 32, 33, 13, 34, 14, 41.
  • 31/32 are discrete low vs high pressure switches — opposite of 987M, where 31/42 is a band.
  • ABCD polarity, one Evolution control, C required. Do not land a 24V Preferred stat on ABCD.

Hardware

  • AFUE: Up to 96.7–97% Evolution two-stage
  • Sister SKU: Carrier 59TN7

First fire

  1. 1987M = modulating, pressure band. 987T / 986T = two-stage, discrete 31/32.
  2. 2987T is the current two-stage Evolution. 986T is the previous plate.

Do not on Bryant 987T

  • Not 987M modulating. Not 986T previous two-stage Evolution. Not 927T Preferred 24V.
  • 986T stays in the bench as the previous Evolution two-stage.

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 987T 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

  • Distributor HX claims sheet

    dealerUS

    Furnace heat exchanger claims — serial in/out of range

    Serial 2993A00001 – 1808A99999 (in-range); later serials are standard warranty

    Primary or secondary heat exchanger failure · Distributor claim path

    Open factsOpen manufacturer PDF

  • CE Canada Bryant trade-in 2025–26

    ended seasonCanada

    High-efficiency gas furnace trade-in — Bryant Canada

    2025-04 (ended 2026-04-30)

    Failed 340–355 family secondary within 20 years of install · Trade-in (ended)

    Open factsOpen manufacturer PDF

  • 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