The Maxitrol TD121 Temperature Selector is a critical control component designed for Selectra Series 21 and 31 electronic gas modulation systems. Specifically engineered for make-up air heating and indirect-fired units with atmospheric burners, this remote selector provides precise setpoint management within a 55-90 degrees F range. Unlike standard thermostats, the TD121 functions as a remote setpoint adjuster, communicating directly with the A1010 or A1011 series amplifiers to regulate discharge air temperature through the modulation of MR valves. This ensures a stable heat output and prevents the common temperature swings associated with cycling systems. For optimal system performance, the TD121 must be paired with a compatible TS121 discharge air sensor sharing the same temperature range. It is frequently utilized in industrial duct applications and commercial HVAC systems where remote mounting—such as in a control cabinet or specialized panel—is required to protect sensitive electronics from harsh environments. This selector is compatible with all fuel gases and can be integrated into systems utilizing a T115 room override thermostat for additional space temperature sensitivity. Precise Modulation: Facilitates seamless gas flow adjustment through Selectra modulator-regulator valves for consistent discharge air. Application Versatility: Ideal for direct-fired or indirect-fired make-up air units requiring a 55-90 degree setpoint. System Compatibility: Integration-ready for Series 21 single furnace and Series 31 multi-furnace configurations. Remote Interface: Allows for setpoint adjustment away from the primary unit, increasing accessibility for facility maintenance. Common Questions Can I use the TD121 with a sensor from a different temperature range? No. The Maxitrol TD121 must be matched with a sensor like the TS121 that operates within the same 55-90°F range to ensure linear calibration and accurate signal processing by the amplifier. Where should this remote selector be installed? The selector should be mounted in a protected location, such as a remote control cabinet or an ETD-1 enclosure, away from weather elements and contaminated atmospheres that could damage the internal circuitry. Does this unit control the high-fire ignition directly? The TD121 provides the setpoint signal to the amplifier. High-fire ignition timing (0, 5, or 25 seconds) is determined by the specific amplifier model (e.g., A1010B) installed in your system. 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.
