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The Lennox 18J37 Limit Switch is a critical safety component engineered for high-performance thermal regulation in residential and light industrial furnaces
A steady on light indicates internal ignition control failure
While the diameter is standard
Field technicians prioritize this Robertshaw ignition part because of its durable ceramic insulation and secure mounting bracket
Fenwal 35-615908-223 Control 30067439-890 The Lennox 18J37 Limit SwitchThe Fenwal 35 615908 223 is a 24 VAC microprocessor based Direct Spark Ignition (DSI) control specifically engineered as an Armstrong furnace replacement. Designed for heavy duty gas fired heating applications, this module integrates an onboard inducer blower relay to coordinate combustion airflow before ignition. It features a critical 30 second pre purge and a 30 second inter purge timing cycle, which clears the combustion chamber of residual gases