FieldBench

Bryant

986T

Furnace · 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.

Walk this in Diagnose

This plate

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.

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

  • 24

    Fuse

    warn

    24 V fuse.

    • ABCD miswire, HUM/EAC, valve harness.
  • 31

    High / active-stage PS

    lockout

    High-fire or active-stage prove failed.

    • Does the inducer actually go high?
    • High-fire hose not teed to the low switch.
    • Vent capacity on 100/120 cabinets.
  • 32

    Low-fire PS

    lockout

    Low-stage draft not proven.

    • Trap, collector, low hose, attic PVC.
    • Fix 32 before you chase 34.
  • 33 / 13

    Limit

    warn

    Airflow or rollout.

    • Evolution heat CFM, filter, coil. Rollout manual reset.
  • 34 / 14

    Ignition

    lockout

    No flame prove.

    • HSI, gas, rod. Fix 32 first if both store.
  • ABCD

    Communication

    lockout

    Wall control or outdoor dropped.

    • A/B/C/D, polarity, C, one master.

Workflows

986T vs 987M vs 926T

First minute on an Evolution-looking Bryant.

  1. Plate 987M + modulating valve = 987M chart. 31 is a band.
  2. Plate 986T / 987T + two-stage valve + two PS = stay here.
  3. Plate 926T + 24V stat + model plug = Preferred chart. No ABCD.

32 on Evolution two-stage

No heat, Evolution stat shows pressure / 32.

  1. This 32 is real low-fire draft — not a 987M band.
  2. Two hoses, two switches. Same collector/trap story as 926T.
  3. Then the bus: if the stat is also showing comms, fix ABCD before you condemn a switch.

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

  • carrier-59tn6 — Carrier Infinity two-stage factory twin.
  • bryant-987m — Evolution modulating. Same ABCD plug, different valve, different 31.
  • bryant-926t — Preferred 24V two-stage. Same 31/32 physics, no ABCD.