FieldBench
Models
Bryantac

187B

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.

Diagnose this modelInstall notesBoard cross-refField wiring

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.

Evolution last 10.

Universal swap

No universal

Bryant 187B outdoor. No furnace IFC universal. Replace the OEM outdoor control / contactor / drive by the silk.

Silk: 187B

White-Rodgers

—

ICM

—

Honeywell

—
  • Indoor furnace universals (50A55, 50M56U, ICM282B, ICM2811, S9200U). This is not an IFC.
  • Do not ‘adapt’ a furnace board to an outdoor inverter, defrost PCB, or contactor.

After you pull the dead card

  1. 1Photograph the outdoor silk. Indoor 50A55 / ICM282B / S9200U do not belong here.
  2. 2Contactor units: replace the contactor / cap / HPS — there is no universal outdoor board.
  3. 3Inverter / communicating outdoors: OEM drive only. There is no White-Rodgers or ICM outdoor universal.

Field wiring

Written landings for Bryant 187B. Not a factory schematic.

Evolution two-stage · ABCD
ABCD (two-stage scroll, not inverter)R-410A

Bryant 187B class. Evolution communicating two-stage. ABCD like 191VAN — but there is no inverter drive and no Y1/Y2 Preferred landing.

Written circuit description only — FieldBench does not redraw maker schematics. Example: R to W closes on a heat call; verify 24V at W1 before you change the IFC.

Open manufacturer PDF

This indoor

Evolution indoor on ABCD. 148TAN Preferred Y1/Y2 is the other Bryant two-stage.

Evolution ABCD

187B / Evolution two-stage outdoor. Not 148TAN Preferred.

Infinity / Evolution wall control

Four-wire ABCD. D is 24V hot, not Y.

  • ADataData
  • BDataData
  • C24V common24V
  • D24V hot — not a cool call24V

Infinity / Evolution indoor

Same ABCD. Indoor CFM is serial. A Comfort 59SC5 does not belong here.

  • ADataData
  • BDataData
  • C24V common24V
  • D24V hot24V

Outdoor communicating drive

ABCD (or the outdoor comm harness). No Y contactor. No dual cap.

  • ADataData
  • BDataData
  • C24V common24V
  • D24V hot — still not Y24V

Outdoor line

208/230 through the disconnect to the contactor line side.

  • L1LineLine
  • L2LineLine
  • GNDEquipment groundLine

Landing

  • DataStat A/B/C/Dindooroutdoor

    Evolution bus. Staging is serial, not Y2.

  • LineL1 / L2outdoor

    208/230

Prove it

  • Evolution event list. The wall control names the outdoor and the stage.
  • If someone landed Y1/Y2 because it is two-stage, that is the 148TAN diagram.

Do not

  • Do not use the 148TAN Preferred Y1/Y2 diagram on 187B.
  • Do not treat this as 191VAN. There is no inverter to reset.

ABCD is the published Evolution control.

Sequence

  1. 1

    Low

    Evolution requests low. Two-stage scroll on low.

  2. 2

    High

    Evolution requests high. Head and SC should rise.

Faults on this IFC

Step 1, then 2, then 3. Expected reading and the fail branch sit under each check.

HPS

High pressure

lockout

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

  1. 1 Heat rejection first

    On Bryant 187B high pressure is outdoor airflow until proven otherwise. Fan running the right direction, coil clean, fins not folded, no recirc over a fence or through a garage. Outdoor fan running? Coil dirty, recirc, bent fins.

    Expect: OD fan on, coil clean, discharge air leaving the top/side freely.

  2. 2 Head, subcooling, and liquid line

    Liquid pressure and liquid-line temperature → SC. High head + high SC = overcharge or non-condensables. High head + low SC = restriction or a dying compressor. Do not add gas because suction is low. Subcooling vs indoor TXV sheet. Liquid-line drier / restriction.

    Expect: SC vs the metering device on this plate (TXV ≠ piston).

  3. 3 Restriction vs the switch

    Drier, liquid-line kink, TXV inlet screen, or a non-feed indoor coil will stack head. Ohm / jumper-test the HPS only as a momentary prove, then restore it. A switch that opens on a known-good charge and clean coil is the switch. Do not keep resetting HPS into a locked fan.

    Expect: HPS closed at a normal liquid pressure for this refrigerant and OD ambient.

LPS

Low pressure / freeze

lockout

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

  1. 1 Airflow and freeze before you add gas

    On Bryant 187B low pressure / freeze is indoor airflow or a starved coil until proven otherwise. Filter, blower, dirty A-coil, closed supplies. In heat mode, a iced outdoor coil is the same family. Indoor filter, blower, coil freeze. Do not add gas on a frozen coil.

    Expect: Indoor air moving. Coil not iced. OD coil clear in heat.

  2. 2 SH / SC after a thaw

    Thaw fully. Then SH and SC vs the metering device. Low charge ices a piston. A TXV stuck closed ices with high SH. A restriction downstream of the ports fakes a low-charge chart. TXV / restriction. Weigh-out if the history is a leak.

    Expect: SH/SC in range for this refrigerant and device after a stable 10-minute run.

  3. 3 Leak, TXV, then the LPS

    Weigh-in if the chart says undercharge. Soap / electronic leak on joints and the coil. LPS that opens on a known-good charge and a clear coil is the switch — momentary test only, then restore. Low ambient and wind can nuisance-trip LPS on a light load — still prove charge.

    Expect: Charge on the nameplate. LPS closed at a normal suction for this OD ambient.

Comm

Indoor/outdoor data

lockout

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

  1. 1 Data pair, not 24 V

    On Bryant 187B indoor/outdoor comm is a data pair (AB, S1/S2, U, ComfortBridge, ComfortLink — whatever THIS plate uses). It is not a 24 V Y. Check polarity, continuity, and that nobody landed it on R/C. Data pair polarity and splices. This is not 24V Y.

    Expect: Pair continuous, not shorted to chassis, polarity per the diagram.

  2. 2 Power both ends, then the outdoor status

    Indoor transformer and outdoor control both alive. Read the outdoor LED / 7-seg. Water in the outdoor control is the usual dead-end after a storm. Indoor IFC family must be GMVC / AVPTC communicating. GR9T96 / GMEC96 / GMSS96 cannot be the ComfortBridge indoor.

    Expect: Both controls powered. Outdoor showing a comm or address state, not a blank board.

  3. 3 Address / bias, then the control

    Communicating plates need a matching indoor address and sometimes a terminating bias. Swap is last: known-good pair + power both ends + correct address. One master on the bus. Outdoor board power before you condemn the indoor IFC.

    Expect: Indoor sees the outdoor. No comm code after a power cycle.

Workflows

187B stuck on low

Runs but never makes design-day capacity.

  1. 1 Prove the call and the live code

    Evolution control actually requesting high? A Preferred stat on this outdoor is the wrong bus on most jobs.

    Expect: Write whatever Evolution two-stage outdoor — ABCD, not a Preferred InteliSense board is showing. Evolution last 10.

    If fail: No call at the IFC → stat / harness. Do not change gas parts.

  2. 2 Isolate the first failed step in the sequence

    If it was landed 24V, prove Y2 at the outdoor. Mixed Evolution outdoor + 926T indoor is a real field pair.

    Expect: High: Evolution requests high. Head and SC should rise.

  3. 3 Confirm with a number, then the next part

    This is not 191VAN. There is no drive to reset and no weigh-in-only finish.

    Expect: 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.

    If fail: Stay on this plate. The out-of-range reading is the part.

    If pass: Reading in range → the next step in this workflow is the repair.

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.

Related plates

Install this plate

Install Bryant 187B as Evolution · two-stage communicating AC.

Evolution · two-stage communicating AC

This plate — not the sister SKU

  • Not 191VAN / 180B (inverter, no discrete Y2). Not 148TAN (Preferred two-stage, 24V Y1/Y2 / InteliSense). Not 280ANV (HP). Not 146SAN single-stage.
  • Techs file 187B under 148TAN because both say two-stage Bryant. Evolution ABCD ≠ Preferred Y1/Y2.
  • 191VAN is the inverter Evolution. Different outdoor entirely.

Control on this outdoor

  • 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.

Hardware

  • 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

First fire

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

Do not on Bryant 187B

  • Not 191VAN / 180B (inverter, no discrete Y2). Not 148TAN (Preferred two-stage, 24V Y1/Y2 / InteliSense). Not 280ANV (HP). Not 146SAN single-stage.
  • Techs file 187B under 148TAN because both say two-stage Bryant. Evolution ABCD ≠ Preferred Y1/Y2.
  • 191VAN is the inverter Evolution. Different outdoor entirely.

Maker literature

FieldBench does not host manufacturer files. Each link opens the maker’s own literature page in a new tab.

  • Bryant document searchLiterature searchEnter the full Bryant plate (926TB60100V21, 987MA…). Owner PDFs are public; many I/Os are dealer-gated.Open manufacturer PDF
  • Bryant document searchLiterature searchSearch Bryant 187B on the maker’s literature page.Open manufacturer PDF

Warranty and bulletins

Affected models, serial range, symptom, remedy, date. Maker files open on the manufacturer site.

All bulletins

  • Residential limited warranty

    warranty sheet

    Carrier / Bryant registered heat-exchanger terms

    Current 59-series / Evolution / Preferred registered warranty · Limited warranty certificate

    Open factsOpen manufacturer PDF

  • Dealer portals

    dealer

    Where remaining service letters live

    Current-year service letters not on a public literature page · Maker dealer portal

    Open factsOpen manufacturer PDF