OEM Carrier 40VA Control Transformer for Model C4850C50AY03661

This OEM control circuit transformer (part# HT01BD236) is the factory-specified replacement for the Carrier C4850C50AY03661 packaged unit. The transformer steps down 120V line voltage to the 24V AC signal required by the thermostat, control board, contactor coil, and gas valve. When this component fails, the entire low-voltage control circuit goes dead — your thermostat goes blank, the system stops responding to any call for heating or cooling, and no fault codes will even appear on the board because it has no power to display them.

• Specs: 40VA rating | Primary: 120V AC | Secondary: 24V AC | OEM part number HT01BD236 | Factory-matched for Carrier C4850C50AY03661 packaged units
• OEM vs Generic: This is a genuine OEM Carrier transformer wound to exact VA and voltage tolerances. Generic aftermarket transformers frequently under-deliver on VA capacity, causing nuisance tripping of the internal thermal overload fuse under normal system load — especially on units with economizers or multiple control accessories.
• Install difficulty: 2/5 — Shut off all power at the disconnect and breaker before beginning. Tools needed: flathead and Phillips screwdrivers, 1/4" nut driver, multimeter. Verify 0V at primary terminals before touching wiring. Photograph or label all low-voltage wiring connections before disconnecting the secondary leads.
• Warranty: 1-year OEM factory warranty against defects in materials and workmanship. In-stock units ship same business day from our warehouse when ordered before 3PM local time.

Compatibility: Designed and factory-matched for the Carrier C4850C50AY03661 packaged unit. Always verify your existing transformer's VA rating and primary/secondary voltages on the unit data plate or wiring diagram before ordering. If you're unsure about fitment, our HVAC parts specialists will verify compatibility before your order ships — no guesswork, no returns.