FieldBench

Bryant

187B

AC · Evolution · two-stage communicating AC

Bryant Evolution two-stage air conditioner. ABCD to the Evolution control. Two-stage scroll — not an inverter and not Preferred InteliSense. Do not treat it like 148TAN Y1/Y2.

Not 191VAN / 180B (inverter, no discrete Y2). Not 148TAN (Preferred two-stage, 24V Y1/Y2 / InteliSense). Not 280ANV (HP). Not 146SAN single-stage.

Walk this in Diagnose

This plate

Stages
Two-stage scroll · Evolution capacity request
Bus
Evolution ABCD. Not a leftover single-stage Y.
Refrigerant
R-410A on this generation
Sister
Carrier 24TPA is Preferred-class — this 187B is Evolution

This board

Evolution two-stage outdoor — ABCD, not a Preferred InteliSense board

  • Evolution events name outdoor faults. There is no inverter L-code set like 191VAN.
  • High stage is a communicating request, not a Y2 wire on a typical Evolution hookup.
  • If the indoor is 926T Preferred, this pair was often landed 24V Y1/Y2 — read the actual diagram.

Sequence

  1. Low. Evolution requests low. Two-stage scroll on low.
  2. High. Evolution requests high. Head and SC should rise.

Faults on this IFC

  • HPS

    High pressure

    lockout

    Outdoor airflow, overcharge, or restriction opened the high-pressure switch.

    • Outdoor fan running? Coil dirty, recirc, bent fins.
    • Subcooling vs indoor TXV sheet. Liquid-line drier / restriction.
    • Do not keep resetting HPS into a locked fan.
  • LPS

    Low pressure / freeze

    lockout

    Suction dropped out — charge, indoor airflow, or TXV.

    • Indoor filter, blower, coil freeze. Do not add gas on a frozen coil.
    • TXV / restriction. Weigh-out if the history is a leak.
    • Low ambient and wind can nuisance-trip LPS on a light load — still prove charge.
  • Comm

    Indoor/outdoor data

    lockout

    ComfortBridge data pair only. Invalid as a diagnosis on a 24V Y1/Y2 hookup.

    • Data pair polarity and splices. This is not 24V Y.
    • Indoor IFC family must be GMVC / AVPTC communicating. GR9T96 / GMEC96 / GMSS96 cannot be the ComfortBridge indoor.
    • One master on the bus. Outdoor board power before you condemn the indoor IFC.

Workflows

187B stuck on low

Runs but never makes design-day capacity.

  1. Evolution control actually requesting high? A Preferred stat on this outdoor is the wrong bus on most jobs.
  2. If it was landed 24V, prove Y2 at the outdoor. Mixed Evolution outdoor + 926T indoor is a real field pair.
  3. This is not 191VAN. There is no drive to reset and no weigh-in-only finish.

Test points

Charge
Nameplate + line-set adders. SC per indoor TXV sheet.
Y1 / Y2
24V pair: both present on high stage. Communicating pair: data, not 24 VAC.
Outdoor board
LED/display before the disconnect. Codes die when you pull power.

Gotchas

  • Techs file 187B under 148TAN because both say two-stage Bryant. Evolution ABCD ≠ Preferred Y1/Y2.
  • 191VAN is the inverter Evolution. Different outdoor entirely.

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