OEM Carrier 40VA Control Transformer HT01BD236 for Model C4850C50AY05051

This OEM control transformer (part# HT01BD236) is the factory-specified replacement for the Carrier C4850C50AY05051 packaged unit. The transformer steps down 120V line voltage to the 24V signal required by the thermostat, contactor coil, and all low-voltage control circuits. When it fails, the entire control system goes dark — the thermostat shows no power, the unit will not respond to any call for heating or cooling, and you may find a blown 3A or 5A fuse on the control board. A failed transformer is often misdiagnosed as a bad control board, so always check secondary voltage (should read 24–28VAC) before replacing more expensive components.

• Specs: 40VA rating | Primary: 120VAC | Secondary: 24VAC | OEM part number HT01BD236 | Factory-matched winding tolerances for stable 24V output under full load
• OEM vs Generic: The OEM HT01BD236 transformer uses factory-spec copper windings and thermal overload protection rated for continuous HVAC duty. Generic transformers frequently under-deliver VA capacity, causing nuisance voltage drops that trigger false lockouts and shorten contactor coil life.
• Install difficulty: 2/5 — Shut off power at the disconnect before starting. Tools needed: flathead and Phillips screwdrivers, wire stripper, multimeter. Note primary and secondary wire colors before disconnecting, and verify secondary output reads 24–28VAC after installation before closing the panel.
• Warranty: 1-year OEM factory warranty. In stock and ships same business day from our warehouse.

Compatibility: Designed for the Carrier C4850C50AY05051 packaged unit. Verify the existing transformer's VA rating and primary/secondary voltages on your unit's wiring diagram or data plate before ordering. If your unit has a 40VA transformer and runs on a standard 120V/24V control circuit, this is a direct drop-in replacement. Have your model and serial number ready — our fitment team is available to confirm compatibility before you order.