OEM Carrier Control Transformer 40VA 208/240V to 24V — HT01BD209 for Model PY4GPAA42090AA

This OEM Carrier control transformer (part number HT01BD209) is the factory-specified replacement for the Carrier PY4GPAA42090AA packaged unit. The transformer steps down 208/240V line voltage to the 24V DC signal required to power your thermostat, control board, contactor coil, and all low-voltage safety circuits. When this transformer fails — due to age, a shorted control wire, or a wiring fault — the result is a completely unresponsive system: the thermostat goes dark, the unit won't respond to any calls for heating or cooling, and the contactor will not pull in.

• Specs: 208/240V Primary | 24V Secondary | 40VA Rating | 50/60 Hz | Factory OEM part number HT01BD209 | Also cross-references 4000A46E07AE28
• OEM vs Generic: This genuine Carrier OEM transformer is wound to exact factory VA and voltage tolerances. Aftermarket units often underperform under full 24V load, causing nuisance lockouts or premature failure of downstream control boards.
• Install Difficulty: 2/5 — Shut off all power at the disconnect and breaker before starting. Tools needed: flathead and Phillips screwdrivers, needle-nose pliers, multimeter (to verify 24V output post-install). Label and photograph all low-voltage wiring before disconnecting. The transformer mounts via two screws inside the control box; swap wire-for-wire and restore power to test.
• Warranty: 1-year OEM factory warranty. In stock and ships same business day from our warehouse.

Compatibility: Direct OEM replacement for Carrier model PY4GPAA42090AA. Also replaces superseded Carrier part numbers HT01BD207, HT01CN232, and 9076-00. Verify your unit's control circuit voltage (208/240V primary, 24V secondary) on the data plate before ordering. Our fitment team is available to confirm compatibility before you buy — order with confidence.