OEM Carrier 40VA Control Transformer for Model C4850C50AJ05051 — Part# HT01BD236

This OEM control transformer (part# HT01BD236) is the factory-specified replacement for the Carrier C4850C50AJ05051 packaged unit. The transformer steps down line voltage (120V) to the 24V AC signal that powers your thermostat, control board, and all low-voltage switching circuits. When this component fails, the entire control circuit goes dark — your thermostat shows a blank screen, the system refuses to respond to any call for heating or cooling, and no fault codes are generated because the board itself has no power. It is often the first component to check when nothing works at all.

• Specs: 40VA rating | 120V primary → 24V secondary | Factory-matched impedance and core construction | Class 2 output for low-voltage control circuits | OEM part number HT01BD236
• OEM vs Generic: OEM transformers are wound to exact factory VA and voltage tolerances, protecting downstream control boards from voltage fluctuations. Generic units frequently run under-rated VA, causing overheating, nuisance tripping, and premature control board failure — costing far more than the transformer itself.
• Install difficulty: 2/5 — Disconnect all power before beginning. Tools needed: flathead and Phillips screwdrivers, multimeter, wire nuts or spade connectors. Confirm primary and secondary voltages with a multimeter after installation before restoring full power. Label all wires before disconnecting the old unit.
• Warranty: 1-year OEM factory warranty against defects in materials and workmanship. Ships same business day from our stocked warehouse.

Compatibility: Designed for the Carrier C4850C50AJ05051 packaged unit. Verify your existing transformer's VA rating, primary voltage, and secondary voltage on the unit's data plate or wiring diagram before ordering — mismatched VA ratings can damage control boards. Our parts specialists are available to confirm fitment before you purchase. Order today and your part ships the same business day.