OEM Carrier 40VA Control Transformer for Model C4850C48AY02551

This is the OEM factory-specified control circuit transformer (part# HT01BD236) for the Carrier C4850C48AY02551 packaged unit. The transformer steps down line voltage (120V) to the 24V AC signal required to power the thermostat, control board, contactor coil, and all low-voltage safety circuits. When the transformer fails, the entire control circuit goes dead — the thermostat goes blank, the system refuses to respond to any call for heating or cooling, and no contactors or valves will energize. A failed transformer is often misdiagnosed as a control board or thermostat issue, so always verify 24V output at the secondary terminals before replacing other components.

• Specs: 40VA rating | Primary: 120V AC | Secondary: 24V AC | OEM part number HT01BD236 | Factory-matched for Carrier C4850C48AY02551 packaged units
• OEM vs Generic: OEM transformers are wound to exact VA and voltage tolerances, ensuring stable 24V output under full load. Undersized or off-tolerance generic transformers can overheat, trip their internal fuse, or deliver low voltage that causes erratic relay and board behavior.
• Install difficulty: 2/5 — Shut off all power to the unit before beginning. Tools needed: multimeter, flathead and Phillips screwdrivers, wire nuts or spade connectors. Test secondary output (24V ±10%) before powering on. Always check for a shorted low-voltage wire that may have blown the original transformer before installing the new one.
• Warranty: 1-year OEM factory warranty. In stock and ships same business day from our warehouse.

Compatibility: This transformer is factory-specified for the Carrier C4850C48AY02551 packaged unit. Confirm your unit's data plate shows 120V control circuit voltage and cross-reference OEM part number HT01BD236 before ordering. Need fitment confirmation? Our HVAC parts specialists verify compatibility before you buy — just reach out before placing your order.