Description
Rheem-Ruud 42-105499-07K Low Fire Pressure Switch Overview
The Rheem-Ruud 42-105499-07K is an OEM replacement pressure switch engineered for low-fire operation in Rheem and Ruud gas furnaces. Set at a -0.40″ W.C. trip point, this switch monitors the negative pressure generated by the draft inducer motor to verify proper venting before allowing the ignition sequence to proceed — a critical safety function that protects both equipment and occupants.
How It Works
The pressure switch is a normally open (N.O.) safety device that closes when the draft inducer establishes adequate negative pressure in the flue/venting system. If the required pressure is not achieved — due to a blocked flue, failed inducer motor, or restricted vent — the switch remains open and prevents the gas valve from energizing, shutting down the heating cycle safely.
Key Features
- OEM Rheem-Ruud replacement part — SKU 42-105499-07K
- Low-fire set point: -0.40″ W.C. (inches of water column)
- Designed for two-stage or staged-combustion Rheem/Ruud gas furnaces
- Monitors draft inducer pressure to confirm safe venting before ignition
- Normally open (N.O.) contact configuration
- Direct OEM fit for precise, reliable installation
- Helps prevent unsafe furnace operation due to blocked or restricted venting
Application
- Compatible with select Rheem and Ruud gas furnace models requiring a -0.40″ W.C. low-fire pressure switch
- Intended for use in residential and light-commercial forced-air gas furnace applications
- Always verify compatibility with your specific furnace model number before installation
Installation Notes
Replace only with the correct OEM part number to maintain proper safety switch operation. Consult the furnace service manual for wiring diagrams and pressure switch location. If the switch fails to close under normal operating conditions, inspect the inducer motor, vent tubing, and flue system for blockages before replacing the switch.
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