Bryantfurnace

986T

Evolution · two-stage · communicating 96%

Bryant Evolution two-stage 96% (factory twin of Carrier 59TN6). 987T is the current Evolution two-stage refresh — same idea. ABCD bus plus a two-stage gas valve and dual pressure switches. Not modulating like 987M. 31/32 here are low vs high PS.

Not 987M (modulating % — pressure band). Not 926T Preferred 24V (no ABCD, model-plug VS). Swapping an Evolution stat onto a 926T does not make it a 986T.

Diagnose this model Install notes Board cross-ref Field wiring

AFUE

Up to 96.7% two-stage condensing

Staging

Two-stage valve · two-speed inducer · dual pressure switches

Bus

Evolution ABCD — capacity request is serial, valve is still two-stage

Sister SKU

Carrier 59TN6 · Bryant 987T current two-stage Evolution plate

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 communicating. 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.
926T Preferred. 987M modulating card.

After you pull the dead card

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

Field wiring

Written landings for Bryant 986T. 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

1Power. L1 / N → IFC120V
2Call. Data pair or 24V W → IFCBus or 24V
3Draft. IFC → inducer → proveTwo-stage PS or a pressure band
4Ignite. IFC → HSI → valve120V igniter
5Blow. IFC → serial ECMNo tap, no cap

This indoor

Evolution two-stage. Same ABCD.

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
Call
Wall control requests a stage over ABCD. Valve is still two-stage (low then high).
2
Low prove
Low inducer → low PS (32). Same physics as 926T, different bus.
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.

Fuse

warn

24 V fuse.

1 Find the 24 V short before you replace the fuse
On Bryant 986T 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 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 If it blows with the harness off
Short is on the Bryant 986T 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.

High / active-stage PS

lockout

High-fire or active-stage prove failed.

1 Prove inducer and the live code
Do not pull power — that clears the Bryant 986T 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 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 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.

Low-fire PS

lockout

Low-stage draft not proven.

1 Prove inducer and the live code
Do not pull power — that clears the Bryant 986T 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 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 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 Treat this as flame outside the exchanger
Do not reset the Bryant 986T 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 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 Reset only after the cause is fixed
Manual-reset rollout. Recurring rollout on Bryant 986T 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 Watch one full try — do not reset
Write the Bryant 986T 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 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 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 Data pair, not 24 V
On Bryant 986T 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 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 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

986T vs 987M vs 926T

First minute on an Evolution-looking Bryant.

1 Prove the call and the live code
Plate 987M + modulating valve = 987M chart. 31 is a band.
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 Isolate the first failed step in the sequence
Plate 986T / 987T + two-stage valve + two PS = stay here.
Expect: Low prove: Low inducer → low PS (32). Same physics as 926T, different bus.
3 Confirm with a number, then the next part
Plate 926T + 24V stat + model plug = Preferred chart. No ABCD.
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.

32 on Evolution two-stage

No heat, Evolution stat shows pressure / 32.

1 Prove the call and the live code
This 32 is real low-fire draft — not a 987M band.
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 Isolate the first failed step in the sequence
Two hoses, two switches. Same collector/trap story as 926T.
Expect: Low prove: Low inducer → low PS (32). Same physics as 926T, different bus.
3 Confirm with a number, then the next part
Then the bus: if the stat is also showing comms, fix ABCD before you condemn a switch.
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

987T is the current Evolution two-stage plate — use this chart, not 987M.
Carrier 59TN6 is the factory twin.
A 926T InteliSense job is not this furnace.

Related plates

Install this plate

Install 986T / 987T as Evolution two-stage. ABCD bus + discrete 31/32 — not 987M modulation.

Cat IV PVC · two-stage valve · dual PS · Evolution ABCD · 987T is the current refresh

Bus vs valve

Evolution wall control on ABCD. Same plug as 987M, different valve and different 31 meaning.
Two-stage gas, two-speed inducer, discrete pressure switches — 31/32 physics like 926T, control like 987M.

First fire

1Pair the Evolution control. Then a low-stage heat call (32 path) and a high-stage call (31/high).
2Do not commission this with a Preferred 24V stat as the primary control.

Do not on Bryant 986T

Do not apply 987M pressure-band setup.
Do not treat a 926T InteliSense stat as this ABCD bus.

Maker literature

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

986T product pageProduct pageOpen manufacturer PDF
987T product page (current two-stage Evolution refresh)Product pageOpen manufacturer PDF
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 986T 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 facts Open manufacturer PDF
CE Canada HX guide
dealerCanada
Canada furnace heat exchanger claim options
2023-02-20
Heat exchanger failure — Canada · Canada distributor program
Open facts Open 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 facts Open manufacturer PDF
Residential limited warranty
warranty sheet
Carrier / Bryant registered heat-exchanger terms
Current 59-series / Evolution / Preferred registered warranty · Limited warranty certificate
Open facts Open manufacturer PDF
Dealer portals
dealer
Where remaining service letters live
Current-year service letters not on a public literature page · Maker dealer portal
Open facts Open manufacturer PDF