White-Rodgers 1F51N-619 Thermostat This is an SPST (Single

This is an SPST (Single Pole Single Throw) switch with a Normally Open (NO) contact function that closes on rising pressure

The Robertshaw 5500-136 Infinite Switch is a vintage-spec

The positive dead-end lock-up capability is essential for safety

In this context

White-Rodgers 1F51N-619 Thermostat This is an SPST (SingleThe White Rodgers 1F51N 619 is a heavy duty, low voltage evaporative cooler thermostat engineered for precise performance in 1C (cooling only) applications. Designed as a direct, mercury free replacement for legacy models like the 1F51 619, 1F51W 619, and 1D51W 632, this mechanical thermostat features a rugged snap action switch rated for 24VAC systems. It provides a specialized interface for swamp cooler operation, including a system switch with OFF,