OEM Carrier 40VA Control Transformer for Model C4850C48AY02051

This OEM step-down transformer (part# HT01BD236) is the factory-specified replacement for the Carrier C4850C48AY02051 packaged unit. The transformer steps down 120V line voltage to the 24V signal required to power the thermostat, control board, contactor coil, and every other low-voltage control circuit in your system. When the transformer fails — due to a shorted wire, failed component, or overload — absolutely nothing responds: no thermostat display, no fan, no heat, no cooling. If you're measuring zero or severely reduced voltage on the 24V secondary side, this transformer is the likely culprit.

• Specs: 40VA rating | Primary: 120V | Secondary: 24V | OEM part number HT01BD236 | Factory-matched impedance and thermal protection
• OEM vs Generic: This OEM unit matches the exact VA rating and thermal cutout spec of the original. Undersized or off-spec generic transformers can fail rapidly when control circuit loads spike, or cause nuisance lockouts from voltage sag across the 24V circuit.
• Install difficulty: 2/5 — Disconnect power at the breaker before proceeding. Tools needed: flathead and Phillips screwdrivers, multimeter, wire nuts or terminal connectors. Label and photograph all wiring connections before removing the original transformer. Verify no downstream short exists before energizing the replacement — a shorted wire will blow the new transformer immediately.
• Warranty: 1-year OEM factory warranty. In-stock and ships same business day from our warehouse.

Compatibility: Engineered and factory-tested for the Carrier C4850C48AY02051 packaged unit. Always confirm voltage ratings and VA on your unit's data plate before ordering. Our technical team is available to verify fitment — call or chat before you order. Order by 3PM local time for same-day shipping.