Trane BRD4874 Board 321894-706 While the S21535 is a

While the S21535 is a widely used Aaon HVAC part

The ASCO 8210G88 Solenoid Valve is a high-performance 2-way normally closed solenoid valve designed for demanding general service applications

Smaller 1/2" to 1-1/4" valves or the VB-7xxx series typically require the AV-391 or AV-393 linkages

The Robertshaw 720-055 is a professional-grade 24V hot surface ignition gas valve engineered for versatile performance in residential central heating

This helps verify the functionality of the 24V AC reversing valve signal and ensures the outdoor fan cycles off correctly during the defrost sequence

Trane BRD4874 Board 321894-706 While the S21535 is aThe Trane BRD4874 Dual Hi Voltage Binary Input Board (MPN: BRD4874, also identified as X13650734060) is a critical interface module for Trane chiller controls, specifically engineered for Tracer CH530 and Tracer TD7 automation platforms. This OEM board acts as a precise signal translator, converting high voltage binary inputs from external field devicessuch as pressure switches and safety relaysinto digital data the HVAC control module can process.