OEM Carrier 40VA Transformer 120V–24V for Model PG9MAB036080AASA (HT01BC116 / HT680054)

This OEM control-circuit transformer is the factory-specified replacement for the Carrier PG9MAB036080AASA gas furnace. It steps down 120V line voltage to the 24V AC signal that powers your thermostat, gas valve, control board relays, and all low-voltage switching circuits. When the transformer fails — due to a shorted low-voltage wire, a failed component drawing excess current, or simple age — the entire control circuit goes dead: the thermostat goes blank, the furnace will not respond to any call for heat, and no error codes will flash because there is no power to display them.

• Specs: 40VA rating | Primary: 120V AC | Secondary: 24V AC | 60 Hz | Foot-mount configuration | Wire lead connections | Integrated 3A fuse protection on select configurations
• OEM vs Generic: This is a genuine OEM-grade replacement (current superseding part HT680054) sourced from Carrier's factory-authorized supply chain. Generic transformers are frequently wound to looser VA tolerances and may not maintain stable 24V output under load, causing nuisance lockouts and premature board failure.
• Install difficulty: 2/5 — Shut off power at the breaker and confirm 0V with a multimeter before touching any wiring. Label or photograph all wire connections before disconnecting. Tools needed: flat-head screwdriver, needle-nose pliers, multimeter. Before replacing the transformer, check for shorted low-voltage wiring — a wiring fault will blow the new transformer immediately.
• Warranty: 1-year OEM manufacturer warranty. In-stock and ships same business day from our warehouse.

Compatibility: Designed for the Carrier PG9MAB036080AASA gas furnace and cross-references to a wide range of Carrier, Bryant, and Payne furnace models using the HT01BC116 or HT680054 transformer. Also supersedes part numbers HT01BC115, HT01BB126, HT01CT120, HT01BC120, and HT01AW115. Always verify primary/secondary voltage and VA rating on your unit's data plate before ordering. Our team is happy to confirm fitment — just reach out before you buy.