What the Pressure Switch Does
The pressure switch confirms the inducer motor has established proper draft before allowing ignition. This is a critical safety device that prevents dangerous gas buildup.
Stuck Open Causes
- Inducer motor not running or running slow
- Blocked pressure hose
- Blocked flue or intake
- Clogged condensate drain
- Cracked inducer housing
- Failed switch diaphragm
Stuck Closed Causes
- Welded switch contacts
- Debris holding contacts closed
- Incorrect switch rating
Testing Procedure
- Turn off power to the furnace
- Locate the pressure switch near the inducer motor
- Disconnect the hose and check for blockages
- Use a multimeter to test continuity
- Replace if the switch fails to open or close properly
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