OEM Carrier 40VA Control Transformer for Model FIOP200511GA — Part# HT01BD209

This OEM control transformer (part# HT01BD209) is the factory-specified replacement for the Carrier FIOP200511GA unit. The transformer steps down 120V line voltage to the 24V signal that powers your thermostat, control board, contactor coil, and every low-voltage circuit in the system. When it fails, the entire control circuit goes dark — the thermostat loses power, no calls for heat or cooling are processed, and the system will not operate at all. A failed transformer is often mistaken for a thermostat or control board fault, making this a critical first diagnostic step.

• Specs: 40VA rating | 120V primary / 24V secondary | Factory-matched OEM design | Engineered to exact Carrier tolerances for the FIOP200511GA platform
• OEM vs Generic: The OEM HT01BD209 transformer is wound and insulated to Carrier's exact VA capacity and thermal ratings. Generic transformers frequently under-deliver on VA, causing voltage sag under load that triggers nuisance lockouts and premature control board failure.
• Install difficulty: 2/5 — Shut off power at the disconnect and breaker before beginning. Tools needed: flathead and Phillips screwdrivers, wire stripper, multimeter (to verify 24V output after install). Label all wires before disconnecting the old unit.
• Warranty: 1-year OEM factory warranty. In stock and ships same business day from our NationalHVACParts.com warehouse.

Compatibility: Engineered as a direct OEM replacement for the Carrier FIOP200511GA. Always verify primary voltage (120V) and VA rating on your existing transformer's label before ordering. If your system uses a 40VA transformer and matches the FIOP200511GA model designation, this is your part. Our fitment team is available to confirm compatibility before you purchase — just reach out before placing your order.