FieldBench

Carrier

58CVA

Furnace · Infinity 80% · two-stage · metal vent

80% two-stage Infinity furnace. Category I vent (metal), no PVC secondary, no condensate collector. Codes look like other Carrier two-digit charts but the physics are draft-hood / inducer + metal vent, not a 96% trap. A 31 here is chimney/draft, never a drowned collector.

Not 59TP6 / 59MN7 / 59TN6 / 59SC5 condensing. A 31 on 58CVA is metal-vent draft, not a drowned 96% trap. Not 58STA Comfort 80 (24V single-stage, no ABCD) — same vent family, different control.

Walk this in Diagnose

This plate

AFUE
80% class · Category I
Vent
Metal Category I · not PVC · no secondary drain / trap
Staging
Two-stage gas · two-speed inducer · metal-vent draft switch
Bus
Infinity ABCD on communicating SKUs

This board

Infinity / two-digit IFC (80% metal vent)

  • 13/33 limit, 14/34 ignition, 31 pressure/draft, 24 fuse — same numbers as the 96% boards, different vent.
  • No secondary condensate path. Do not pull the trap playbook from a 59TP6, 59SC5, or 59MN7.
  • 31 is Category I draft / inducer / chimney. It is not a 96% trap, not an attic PVC slope, and not a modulating pressure band.
  • Infinity wall control events first when the ABCD control is alive. Board two-digit if the stat is blank.

Sequence

  1. W1 / low. Inducer → draft/pressure switch on metal vent → HSI → low fire. 31 if the metal vent will not prove.
  2. W2 / high. High fire, still Category I draft. Wind and shared chimneys show up here. Still no PVC trap.
  3. Limit. 33 airflow / rollout. 80% A-coils dirty the same as anything else. Held open → 13.

Faults on this IFC

  • 24

    Secondary fuse open

    warn

    24 V fuse on the IFC.

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

    Draft / PS

    lockout

    Metal vent will not prove. This is not a 96% trap.

    • Chimney liner, cap, common-vent tables, inducer wheel.
    • Not a PVC trap and not a collector box. Do not cut a ‘condensate’ drain that does not exist.
    • PS hose to the inducer housing can hold flue condensate on a long metal run — still Category I, still not a 59SC5 collector.
    • Common-vented water heater: venting table / liner, not a switch.
  • 33 / 13

    Limit

    warn

    Airflow. 80% coils still dirty. 13 is the hardened 33.

    • Filter, AC coil on top, blower, Infinity heat CFM.
    • Rollout: exchanger / burners / flue. Manual reset.
  • 34 / 14

    Ignition

    lockout

    HSI / gas / rod. 14 is the hardened 34.

    • Same prove logic as other Carrier IFCs. Fix 31 draft before a fair 34 test.
  • ABCD

    Communication

    lockout

    Wall control or outdoor dropped (communicating 58CVA SKUs).

    • A/B/C/D, polarity, C required, no 24V on D.
    • Non-communicating 58CVX cousins may be 24V — read the actual board.

Workflows

31 on an 80% Infinity

Do not dump the condensate trap.

  1. This furnace has no secondary drain. Look at the metal vent and the inducer wheel. 31 is not a 96% trap.
  2. Common-vented water heater: the 31 may be a venting table problem, not a switch.
  3. Chimney liner, cap, masonry debris, wind cap. Category I tables — spillage at the draft hood / inducer inlet is a fail.
  4. Then the PS hose to the inducer housing — still can fill with water from flue condensation in long metal runs, but it is not a 96% collector.
  5. Infinity events will say pressure or draft. Believe that over a 59MN7 band story or a 59SC5 trap story.

Which Carrier 80% is this?

Plate is rusty or someone called it a 59-series.

  1. Metal vent, no collector = 80%. PVC + trap = you are on the wrong page (59-series).
  2. ABCD wall control + two-stage 80% = 58CVA / Infinity 80. Single-stage Comfort 80 24V = 58STA.
  3. 58MVP / 355CAV older variable 80% — similar metal-vent 31, different IFC generation. Read that door card.

Test points

Vent
Cat I tables. Spillage at the draft hood / inducer inlet is a fail. No PVC trap to pull.
ABCD
On communicating SKUs: D is not W. C required.
31 hose
Inducer housing tap on metal vent. Water here is flue condensate, not a 96% collector.

Gotchas

  • 58MVP / 355CAV older variable 80% — similar idea, different IFC generation. Read that door card.
  • Bryant 355CAV is the badge twin on many jobs.
  • A tech who just left a 59SC5 will dump the ‘trap’ and miss the chimney liner.

Related plates

  • carrier-58sta — Comfort 80 single-stage 24V — same metal-vent 31, no Infinity bus.
  • carrier-59mn7 — Infinity 96% modulating — 31 there is a condensing band/trap, not Cat I draft.