McDonnell & Miller AF-2 Switch

The McDonnell & Miller AF-2 Air Flow Switch (Part Number 123200) is a specialized low velocity air flow switch engineered to prove fan operation and monitor airflow in critical HVACR systems. Built for durability, this field-proven unit features brass, steel, and aluminum construction, making it ideal for standard commercial and industrial duct environments. The integrated snap acting SPDT switch provides reliable signaling for interlocking blowers, heaters, or exhaust fans. Designed for low-flow sensitivity, the AF-2 model utilizes a large paddle assembly that fits a minimum 8-inch duct but can be field-trimmed to accommodate 6-inch applications.

Contractors often select the McDonnell & Miller 123200 for its straightforward mechanical reliability. The unit includes an external sensitivity adjusting screw that allows for precise calibration of the flow switch actuation point without internal disassembly. Dual electrical knock-outs facilitate flexible SPDT switch wiring from either end of the housing, streamlining low velocity HVAC airflow monitoring. With a maximum duct temperature rating of 300°F (149°C), the AF-2 airflow detector is a robust choice for proving airflow in systems where high-velocity switches fail to actuate.

• Optimized for Low Velocity: Specifically designed to detect movement in low-flow scenarios that standard switches miss.
• Durable Construction: Heavy-duty brass and aluminum components withstand continuous industrial use.
• Field Adjustable: Features a sensitivity adjusting screw for precise onsite setpoint calibration.
• Versatile Duct Compatibility: Standard paddle fits 8" ducts and is trimmable for 6" ductwork installations.
• Flexible Wiring: SPDT snap-acting switch and dual knock-outs simplify electrical integration.

Common Questions

How do I adjust the sensitivity of the McDonnell & Miller AF-2?
Adjustments are made via the external sensitivity screw. Turning the screw clockwise increases the velocity required to actuate the switch, while counter-clockwise decreases the required velocity.

Can the AF-2 be installed in any orientation?
While the switch can be mounted in various positions, it is critical to ensure the paddle is perpendicular to the airflow and that the orientation does not interfere with the mechanical reset of the snap switch.

What is the difference between the AF-1 and the AF-2?
The AF-1 is typically used for medium and high velocity applications, whereas the AF-2 is specifically calibrated for low velocity air flow detection.

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.