FieldBench

Carrier

59SC5

Furnace · Comfort 96 · single-stage · conventional 24V

Carrier Comfort 96 single-stage condensing furnace. 59SC5 / 59SC5A are single-stage gas with a conventional multi-speed or CT blower. 59SC6 keeps single-stage gas and adds an 18-speed blower — still not two-stage, still not Infinity. Conventional 24V thermostat. Two-digit IFC like other Carrier boards, but there is no high-fire pressure switch and no W2 furnace path.

Not 59TP6 (two-stage VS + model-plug staging + dual PS). Not 59MN7 Infinity modulating (ABCD bus, pressure band). A 32 on 59SC5 is the only draft switch, not 'low fire.' 59SC6 is still single-stage gas — the 18-speed blower does not add a second solenoid or a high-fire PS.

Maker PDFs

Walk this in Diagnose

This plate

AFUE
Up to 96% condensing (59SC2 is the 92% Comfort cousin)
Staging
Single-stage gas valve · one inducer speed · one pressure switch
Blower
59SC5: multi-speed / CT. 59SC6: 18-speed ECM (taps / setup, not TP6 model-plug CFM)
Control
Two-digit IFC · conventional 24V (W G Y R C). No ABCD.
Vent
PVC 2-pipe or 1-pipe · condensate collector and trap
Sister SKU
Bryant 915S · 59SC5A revision · 59SC6 18-speed

This board

Two-digit IFC (single-stage Comfort — not TP6, not Infinity)

  • Same Carrier two-digit language that applies to single-stage: 11, 12, 13, 14, 21, 22, 23, 24, 31, 33, 34, 41 (59SC6), 45.
  • There is no high-fire PS and no W2 furnace path. Do not run the 59TP6 32-then-high-fire playbook.
  • Some boards still flash 32 for the single PS path — confirm the door card. 59TP6 uses 32 specifically as low-fire PS. On SC5/SC6, 32 is not a second stage.
  • A live 3 1.6-style CFM readout is a TP6/VS habit. Comfort 96 is not reporting staged CFM that way.
  • Amber LED flash charts from old 80% Comfort boards do not apply.

Sequence

  1. W. Single W only. Inducer on → the one pressure switch must close (31 if it does not) → HSI → single-stage valve → flame (34 if no prove) → heat-speed blower.
  2. No W2. There is no second solenoid and no high-fire switch. A wire on W2 does nothing useful on the furnace side. Do not look for a 32-vs-31 two-stage split.
  3. 59SC6 blower. 18-speed motor follows heat/cool taps or setup, not a 59TP6 model-plug CFM table. 41 is the RPM-out-of-band code on that motor.
  4. Limits. 33 is the open limit/rollout circuit. Held open becomes lockout 13.
  5. Ignition fail. 34 repeats, then lockout 14.

Faults on this IFC

  • 11

    No stored history

    info

    Memory empty or power was cycled.

    • Not a fault. Recreate the W call and watch the live code.
  • 12

    Blower on after power-up

    info

    Powered up on a W call — blower-on delay / 90 s class run.

    • Normal after a brownout. Repeating 12 + 41 on a 59SC6 → 18-speed calibration / static.
  • 13

    Limit lockout

    lockout

    Limit/rollout stayed open. Auto-reset ~3 h on this IFC family.

    • Treat as a hardened 33. Filter, heat speed / 18-speed tap, rise, rollout reset.
  • 14

    Ignition lockout

    lockout

    Hardened 34. Auto-reset ~3 h.

    • HSI, gas, flame sensor, ground. Do not sit on resets.
  • 21

    Gas-heat lockout / model plug

    lockout

    Valve relay fault, or missing/wrong model plug on boards that use one (more likely on 59SC6 18-speed).

    • Valve harness and 24 VAC during trial.
    • If this cabinet has a model plug, it must match THIS Comfort 96 cabinet — do not steal a 59TP6 plug and expect correct CFM.
    • Miswired valve.
  • 22

    Flame with valve off

    hazard

    Flame sense while GV de-energized.

    • Leaking valve. Shut the cock.
  • 23

    PS did not open

    lockout

    The (only) pressure switch is still made when it should be open.

    • Welded switch, water in hose, inducer still spinning when it should be off.
    • One switch — there is no ‘the other PS’ to swap to.
  • 24

    Secondary fuse open

    warn

    24 V fuse on the IFC.

    • Tstat short, HUM/EAC, valve harness. Replace fuse only after the short is gone.
  • 31

    Pressure / draft did not close

    lockout

    Inducer running, the only prove switch is open. This is the single draft path — not ‘low fire’ and not a missing high-fire switch.

    • Trap, collector, PVC slope, wind, inducer.
    • Attic jobs: ice in the vent, dry-siphoned or frozen trap.
    • If the door card also lists 32, treat 32 as this same single PS path — confirm the sticker.
  • 32

    32 on Comfort 96 — the only PS

    lockout

    If this door card lists 32, it is the same single draft switch as 31 — not 59TP6 low-fire and not a missing high-fire hose. One switch, one hose.

    • Count hoses. One = this chart. Two = you are on a TP6/TN6, not SC5.
    • Trap, collector, PVC. Same physics as 31.
    • Do not order a ‘low-fire’ switch for a cabinet that never had a second solenoid.
  • 33

    Limit or rollout open

    warn

    Airflow or flame-containment. Single-stage heat speed, not TP6 model-plug CFM.

    • Filter, coil, return, heat tap (59SC5) or 18-speed heat selection (59SC6).
    • Do not pull a 59TP6 model-plug CFM table onto this motor.
    • Rollout is manual reset — inspect exchanger before you reset.
    • Held open → 13.
  • 34

    Ignition prove fail

    lockout

    Trial without flame sense. Repeats → 14.

    • HSI glow and 120 VAC, gas cock, manifold, flame rod oxide, IFC ground.
  • 41

    Blower RPM out of band

    lockout

    Applies on 59SC6 18-speed / VS-ish motors. Comfort 96 PSC/CT 59SC5 jobs rarely throw a true 41.

    • Confirm it is an 18-speed 59SC6 before you chase a VS model plug.
    • Static, wheel, harness, heat/cool taps or setup — not a 59TP6 plug chart.
    • Filter and coil first.
  • 45

    Control lockout

    lockout

    IFC parked itself.

    • Power reset once after the root code is understood. Repeat 45 = board or persistent input.

Workflows

33 / 13 overheating

Heat runs then drops, or lockout 13 after a long 33.

  1. 33 live vs 13 lockout. 13 needs the wait or a power cycle after the cause is fixed.
  2. This is single-stage heat speed. 59SC5: heat tap / CT profile. 59SC6: 18-speed taps or setup — not a 59TP6 model-plug CFM table.
  3. Filter, A-coil, return. Comfort 96 cabinets still get stuffed media filters and dirty coils.
  4. Rise vs the rating plate. Overfire on a single-stage valve is manifold / orifice, not a stuck high-fire solenoid.
  5. Rollout portion of the 33 circuit: if the rollout is open, stop and inspect. Do not keep resetting.

31 attic PVC / trap

No heat, inducer running, 31 (or a door-card 32 on the same single switch).

  1. One pressure switch. Do not hunt a high-fire hose that is not there.
  2. Trap and collector first — 96% physics. Attic: frozen trap, dry trap, PVC with no slope back to the collector.
  3. Intake/exhaust terminations (bird screen, ice, wind). Long 2" runs that ‘worked last winter’ ice shut.
  4. Hose on the only inducer tap, not cracked, not full of water.
  5. Then inducer 120 VAC and wheel. 23 after it finally runs means the switch never reopened.

Identify SC5 vs TP6

Data plate is dirty or the last tech called every Carrier 96 a 59TP6.

  1. Count pressure switches. One PS = Comfort 96 (SC5/SC6). Two PS = Performance two-stage (TP6) or Infinity two-stage (TN6).
  2. Valve: one solenoid vs two-stage body. W2 on the IFC that actually stages the furnace = not SC5.
  3. Model plug + VS serial motor + 3 1.6 CFM readout = 59TP6. 18-speed tap motor = 59SC6, still this chart.
  4. ABCD wall control = Infinity (59TN6 / 59MN7), not this furnace.
  5. A 32 on SC5 is the only draft switch if the door card lists it. On TP6, 32 is specifically low-fire PS.

Test points

Pressure switch
One switch, one hose. Open with inducer off; must close on a W call. 31 = never closed. 23 = never reopened.
W at IFC
R to W ~24 VAC. No W2 furnace path to wait on.
Heat speed
59SC5 tap/profile vs rise. 59SC6 18-speed heat selection — not a TP6 model-plug CFM number.
Flame sense
µA per Comfort 96 door card (typically ≥ 0.5–1.0 µA class).

Gotchas

  • 59SC6 looks ‘variable’ in the basement and is still single-stage gas. Do not invent a high-fire PS.
  • Bryant 915S uses this Comfort 96 chart. 59TP6 / 926T does not.
  • 59SC2 is Comfort 92 — same single-stage two-digit language, still one PS, still a condensing trap.
  • Do not land an Infinity ABCD stat on this IFC and expect it to become a 59TN6.

Related plates

  • bryant-916s — Bryant Legacy 916S / 915S. Same Comfort 96 single-stage 31/33/34. Type 915S on Diagnose.
  • carrier-59tp6 — Performance 96 two-stage VS — dual PS, W2, model-plug CFM. 32 there is low fire.
  • carrier-59mn7 — Infinity modulating — ABCD bus, pressure band, not a Comfort 24V board.
  • carrier-58sta — Comfort 80 single-stage — same 31 number, metal vent, no PVC trap.