Lennox 18J74 Pressure Switch

The Lennox 18J74 Pressure Switch is a high-precision low ambient pressure switch engineered to regulate head pressure by cycling the outdoor fan motor during cooling cycles. Designed specifically for HVAC professionals, this OEM replacement part ensures your system maintains consistent evaporating temperatures, effectively preventing evaporator coil icing and protecting the compressor from liquid slugging. With an open temperature of 150°F and a close temperature of 275°F, this switch is critical for maintaining performance in heat pumps and air conditioning units like the HP26 series, CHA16, and GCS24 models.

Constructed for heavy-duty field use, the Lennox 18J74 (also referred to as 18J7401) features a robust housing and high-reliability internal contacts. Implementing this head pressure control switch allows for safe cooling operation in low ambient conditions down to 30°F. Using genuine Lennox parts ensures 100% HVAC part compatibility, preserving original factory efficiency ratings and sound quality standards while eliminating the risks associated with generic alternatives.

• System Protection: Actively monitors liquid line pressure to prevent low-pressure conditions that lead to evaporator icing.
• OEM Compatibility: Precision-fit for Lennox heat pumps (HP26-030/036/048) and various residential/commercial series.
• Operational Reliability: Maintains discharge pressure within factory specs to ensure proper refrigerant flow through expansion valves.
• Technician-Friendly: Standardized mounting and electrical terminals for efficient field replacement.

What are the cut-in and cut-out settings for this switch?
This specific low ambient switch is calibrated to open at 150°F and close at 275°F to maintain head pressure during low outdoor temperatures.

Can I use the 18J74 on units with capillary tube metering?
No. Low ambient kits using these switches are designed for systems with expansion valve (TXV) metering devices to prevent liquid migration.

What HVAC error codes are associated with a failing pressure switch?
A faulty switch often triggers "low pressure" or "stuck open" alerts on Lennox communicating thermostats, designated as Service Urgent or Service Soon codes.

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.