FieldBench

Carrier

59TN6

Furnace · Infinity · two-stage · communicating 96%

Infinity two-stage communicating 96% furnace (Bryant 986T). ABCD bus plus a two-stage gas valve and dual pressure switches. Not modulating like 59MN7. Two-digit board codes plus Infinity English on the wall control. 31/32 here are low vs high PS — the same two-stage physics as 59TP6, on a communicating control.

Not 59MN7 (modulating % — pressure BAND, not discrete 31/32). Not 59TP6 (24V Performance — no ABCD, model-plug VS). Swapping an Infinity stat onto a 59TP6 does not make it a 59TN6. Not 59SC5 Comfort single-stage.

Maker PDFs

Walk this in Diagnose

This plate

AFUE
96% condensing two-stage
Staging
Two-stage gas valve · two-speed inducer · dual pressure switches
Bus
Infinity ABCD wall control — capacity request is serial, valve is still two-stage
Blower
Infinity VS ECM
Sister SKU
Bryant 986T

This board

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

  • Infinity wall control Service / Last 10 events first — English names. Board two-digit still flashes 24, 31, 32, 33, 13, 34, 14, 41.
  • 31/32 are discrete low vs high pressure switches. That is the opposite of 59MN7, where 31/42 is a band.
  • ABCD polarity, one Infinity control, C required. Do not land a 24V stat on ABCD.
  • A 59TP6 door card is the wrong card: same 31/32 words, different bus and no model-plug CFM readout.

Sequence

  1. Call. Infinity wall control requests low or high heat over ABCD. IFC runs the two-stage sequence — there is no modulating %.
  2. Low fire. Inducer low → low PS must close (31/32 family) → HSI → low-fire solenoid → flame (34 if no prove) → VS blower per Infinity CFM.
  3. High fire. Inducer high → high PS must close. 32 on this furnace is low-fire draft, not a 59MN7 band miss.
  4. Limit / ign. 33 → 13 limit lockout. 34 → 14 ignition lockout. Same Carrier two-digit hardening as TP6.

Faults on this IFC

  • ABCD

    Communication

    lockout

    Wall control or outdoor dropped off the bus.

    • A/B/C/D landing, polarity, only one Infinity control, no 24V on D.
    • C present. A 24V Performance stat on this IFC will not stage it like a 59TP6.
    • Outdoor pair on the same bus — a dead Greenspeed looks like indoor comm loss until you read events.
  • COMM

    No communication with indoor

    lockout

    Infinity wall control lost the IFC. Last 10 is primary.

    • R to C. A/B polarity. D is not W.
    • One control on the bus.
    • 59TP6 + this stat is the wrong bus — load 59TP6, not this plate.
  • COMM OUT

    No communication with outdoor

    lockout

    Outdoor dropped off ABCD.

    • Same ABCD pair at the outdoor.
    • Contactor-only outdoor will never talk.
    • Setup outdoor ID vs plate.
  • 24

    Secondary fuse open

    warn

    24 V fuse on the IFC.

    • HUM/EAC, valve harness, or 24V landed on ABCD.
    • Replace fuse only after the short is gone.
  • 31 / 32

    Low vs high pressure switch

    lockout

    Two-stage draft path. 31 is the active-stage / draft prove; 32 is low-fire PS. Unlike 59MN7, these are discrete switches.

    • Two hoses, two switches. Do not treat this as a modulating band.
    • 32 = low-fire hose, low inducer, attic PVC/trap/wind.
    • High-fire prove fail is the high PS, not a 59MN7 42 band story.
    • Trap and collector first — 96% physics.
  • 33 / 13

    Limit or rollout

    warn

    Airflow or flame-containment. 13 is the hardened 33.

    • Infinity heat CFM, filter, coil, return.
    • Not a 59SC5 heat tap and not a 59TP6 model plug.
    • Rollout is manual reset — inspect exchanger first.
  • 34 / 14

    Ignition prove fail

    lockout

    Trial without flame sense. 14 is the hardened 34.

    • HSI, gas, rod, ground.
    • If 32 is also stored, fix low-fire draft before you condemn the igniter.
  • 41

    Blower RPM out of band

    lockout

    Infinity VS motor not at commanded CFM.

    • Static, wheel, serial harness, Infinity indoor size / CFM setup.
    • Filter and coil.

Workflows

Identify TN6 vs MN7 vs TP6

Badge is gone or the last invoice just says ‘Infinity 96.’

  1. ABCD bus present? No → 59TP6 / 59SC5, not this page. Yes → Infinity, continue.
  2. Valve and PS: two-stage body + two discrete pressure switches = 59TN6. Modulating valve + transducer / band (no 32 low-fire switch) = 59MN7.
  3. 59TP6 has the two-stage hardware but a 24V stat and a model plug. Putting an Infinity wall control on a 59TP6 does not make it a 59TN6.
  4. Bryant 986T = this chart. Bryant 987M = 59MN7. Bryant 926T = 59TP6.

Infinity no-heat

Wall control is on, house is cold, or the homeowner says the system ‘lost communication.’

  1. Infinity event list first. English text beats guessing the two-digit.
  2. Then the board: 24 fuse, ABCD drop, 31/32 draft, 34 ignition, 33 limit.
  3. C still required. Blank or rebooting control with 0 VAC at C is not a bad IFC.
  4. Do not convert to 24V by jumping W. You will not get a fair two-stage Infinity sequence.

32 low fire on communicating two-stage

Inducer runs, no light-off, or it never leaves low heat.

  1. 32 on 59TN6 is low-fire PS — same physics as 59TP6, different bus. It is not a 59MN7 pressure band.
  2. Low-fire hose only. Trap, collector, attic PVC, intake wind/ice.
  3. Confirm the inducer actually went to low, not a failed high-speed request wearing a 32.
  4. Then ignition (34). A starved low-fire prove will never give a clean 34 test.

Test points

ABCD
Communicating. D is not W. C required.
Pressure switches
Two discrete switches. 32 = low. High-fire has its own hose. Not an MN7 band.
Flame sense
µA per 59TN6 / 986T door card.

Gotchas

  • Same ABCD plug as 59MN7. Wrong chart if you treat 31 as a modulating band.
  • Same two-stage gas as 59TP6. Wrong chart if you look for a model plug and a 24V W2.
  • Bryant 986T is the badge twin. 987M is the modulator.

Related plates

  • bryant-986t — Bryant Evolution 986T / 987T factory twin. Same two-stage ABCD IFC.
  • carrier-59mn7 — Infinity modulating — 31/42 is a band, not low vs high PS.
  • carrier-59tp6 — 24V Performance two-stage — no ABCD. An Infinity stat does not convert it.