York S1-7945-3551 Transformer

The York S1-7945-3551 Transformer is a critical OEM replacement part designed for precision voltage regulation in York, Coleman, and Evcon HVAC systems. This 120V to 24V step-down transformer features a 15VA power rating, providing a stable low-voltage current to reach the control board, contactors, and thermostats. Built as a Class 2 transformer, it ensures proper isolation for the secondary circuit, protecting sensitive electronic components from primary surges. Its compact, robust construction allows for direct fitment in various residential furnaces and packaged RTUs, including DGAT, DGPT, and DLAS series models. For the veteran technician, this unit is a reliable solution for restoring communication between the HVAC control circuit and the diagnostic interface. Whether you are troubleshooting an unresponsive thermostat or a failed contactor coil, the York S1-7945-3551 delivers the consistent 24VAC output required for modern high-efficiency equipment. Ensure all line voltage is disconnected before verifying secondary resistance with a multimeter to confirm circuit integrity.

• OEM Compatibility: Exact drop-in replacement for York and Coleman part number S1-7945-3551, ensuring no modifications are needed during installation.
• High Isolation Efficiency: Engineered as a Class 2 power source to isolate the low-voltage control loop from the 120V primary feed.
• Durable 15VA Rating: Provides sufficient volt-ampere capacity to power modern digital thermostats and standard system relays reliably.
• Broad Application: Compatible with a wide range of furnace models, specifically documented for use in DGAT and DLAS assemblies.

Can I use this 15VA transformer if my old one was 40VA?
No, you should never downsize your VA rating. A 15VA transformer is designed for specific low-load control circuits; using it in place of a 40VA unit will likely cause the windings to overheat and fail under the higher current demand of the system's accessories.

Why does my 24V transformer keep failing immediately after installation?
A total failure shortly after startup usually indicates a direct short in the secondary circuit. Before installing the York S1-7945-3551, check the thermostat wiring for nicks and test the resistance of your contactor coils to ensure they aren't drawing excessive amperage.

Does this unit have an integrated fuse for protection?
This specific model does not typically include an onboard reset button or fuse. Most York systems utilize an inline 3A or 5A automotive-style fuse on the primary control board to protect this transformer from secondary shorts.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.