229809 - Miller 240F Normally Open Thermal Switch 3/4-16 UNF

Precise Thermal Monitoring for Miller Equipment

The Miller 229809 Temperature Switch is a critical component designed to maintain the operational integrity and safety of compatible Miller welding power sources. Engineered to specific OEM standards, this thermal switch operates with a Normally Open (NO) configuration, meaning the electrical circuit remains open during normal operation and closes when the monitored temperature reaches the activation point. This specific unit is calibrated to actuate at 240°F (approximately 115°C), a precise threshold often used to trigger cooling fans or signal thermal overload conditions within the machine's logic board.

Constructed for the rigorous environment of industrial welding, the switch features robust 1/4-inch Fast-On terminals. These spade-style connectors allow for quick, tool-free electrical connections that resist loosening under the high-vibration conditions typical of heavy-duty welding equipment. The body of the switch is threaded with a 3/4-16 UNF pitch, allowing it to screw directly into heat sinks, rectifier assemblies, or transformer windings where thermal monitoring is most critical. This direct physical contact ensures rapid thermal transfer and accurate response times to temperature spikes.

Using genuine Miller replacement parts like the 229809 is essential for preserving the factory warranty and performance specifications of your equipment. Generic thermal switches may have different hysteresis curves or response latencies, which could lead to nuisance tripping or, worse, catastrophic overheating of expensive power components. This switch is a direct replacement for the original part found in various Miller MIG, TIG, and Stick welders, ensuring that your machine's duty cycle protection functions exactly as the engineers intended.

Technical Specifications

• Part Number: 229809
• Function: Temperature Monitoring / Thermal Protection
• State: Normally Open (NO)
• Set Point: 240°F
• Mounting: 3/4-16 UNF Thread