The Maxitrol TD121B Temperature Selector is a critical component for Selectra Series 21 and 31 electronic gas flame modulation systems. Specifically engineered for indirect-fired make-up air units, this remote selector provides precise setpoint control within a 120-170°F temperature range. For a stable discharge air temperature, it must be paired with a TS121B sensor to ensure the resistance curves match the A1010 or A1011 amplifier logic. This hardware eliminates the hunting common in traditional mechanical controls by communicating directly with Modulator-Regulator (M/MR) valves to provide instantaneous gas flow adjustments. As a veteran-preferred HVACR control solution, the TD121B is designed for mounting in control cabinets or remote panels, maintaining a linear gas modulation response across atmospheric burners. Proper field installation requires shielded wiring separated from high-voltage lines to prevent signal interference and ensure accurate thermal regulation in demanding industrial or commercial heating processes. Key Benefits Precise Modulation: Facilitates seamless gas flow adjustment via Selectra electronic controls, avoiding the efficiency losses of "on/off" cycling. Exact Calibration: The 120-170 degrees F range is optimized for high-temperature process air and specific make-up air requirements. System Compatibility: Direct integration with Maxitrol Series 21 systems and works in tandem with mixing tube sensors for accurate duct sensing. Rugged Reliability: Built for technical environments, providing a stable interface for qualified installation in industrial control cabinets. Common Questions Does this selector work with any discharge sensor? No, the Maxitrol TD121B must be matched with a sensor that shares the same 120-170°F color code/range, typically the TS121B, to maintain amplifier calibration. How do I verify the modulating function during commissioning? Using a DC voltmeter on terminals 1 and 2, you should see 0 volts at the maximum temperature setting, with voltage increasing to approximately 20V DC as you rotate toward the minimum setting. Can I run the selector wiring through the same conduit as the blower motor power? It is highly recommended to run control wiring in a separate conduit. Induced voltage from power lines can cause erratic flame modulation or damage the A1010 amplifier. 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.
