ALXT7C

This board

Two-stage outdoor · R-32

• Outdoor board, not AMVC E-codes.
• R-32 nameplate.

Sequence

1. Y1 / low. Outdoor starts low capacity. Indoor blower on low/mid Cool tap (24V) or communicating CFM (ComfortBridge indoor).
2. Y2 / high. Second stage. Head and subcooling should rise into the OEM SC window.
3. Communicating pair. GMVC96 / AVPTC indoor requests capacity on the data pair. No conventional Y needed. A 24V GR9T96 on that same pair is a miswire.

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

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

• Goodman GLXT7C is the twin.

Related plates

• goodman-glxt7c — Goodman-badge twin.
• amana-alxs4b — R-32 single-stage.
• amana-asxc18 — R-410A two-stage predecessor.