OEM Carrier 40VA Control Transformer HT01BD236 for Model C48A405051

This OEM Carrier control transformer (part number HT01BD236) is the factory-specified replacement for the Carrier C48A405051 packaged unit. The transformer steps down 120V line voltage to the 24V signal required by your thermostat, contactor coil, gas valve, and control board. When the transformer fails, the entire control circuit loses power — meaning nothing responds: the thermostat goes blank, the unit won't call for cooling or heating, and no fault codes appear on the board. If you have 120V at the primary but zero volts at the secondary, this transformer is the culprit.

• Specs: 40VA rated | Primary: 120VAC | Secondary: 24VAC | OEM part number HT01BD236 | Factory-matched output for full control circuit compatibility
• OEM vs Generic: This is a genuine OEM Carrier transformer wound to exact VA and voltage tolerances. Generic transformers can sag under load, causing intermittent lockouts, nuisance tripping of the secondary fuse, and premature contactor coil failure — problems that are difficult to diagnose and costly to chase.
• Install difficulty: 2/5 — Disconnect power at the disconnect box and verify zero voltage with a multimeter before touching any wiring. Tools needed: flathead and Phillips screwdrivers, needle-nose pliers, multimeter. Label all low-voltage wires before removing the old transformer. Check and replace the 3A or 5A secondary fuse if it has blown — a shorted load may have caused the original failure.
• Warranty: 1-year OEM factory warranty against defects in materials and workmanship. In-stock and ships same business day from our NationalHVACParts.com warehouse.

Compatibility: Designed for the Carrier C48A405051 packaged unit. Always verify your existing transformer's VA rating, primary voltage, and secondary voltage from the unit data plate or wiring diagram before ordering. Our parts specialists are available to confirm fitment prior to purchase — reach out before you order if you have any questions.