HVACopediaGoodman · Furnace troubleshooting
High stage pressure switch open, furnace on low stage only
What is going on
Induced draft blower runs but the furnace only operates on low stage.
Likely causes
- Pressure switch hose blocked, pinched or connected improperly
- Blocked flue and/or inlet air pipe, blocked drain system, or weak induced draft blower
- Incorrect pressure switch set point or failing switch contacts
- Loose or improperly connected wiring
Check in this order
- Turn power off before repair.
- Replace the pressure switch with the correct part.
- Inspect the pressure switch hose and repair or replace if needed.
- Inspect flue and/or inlet air piping for blockage, length, elbows and termination. Check the drain system.
- Check induced draft blower performance and correct as needed.
- Correct the pressure switch set point or contact action.
- Tighten or correct the wiring connection.
- Replace the induced draft blower with the correct part if it is weak.
Applies to: 34.5 in chassis gas furnaces
More furnace guides
- Airflow lower than demanded, furnace runs on low stage when high stage is expected
- Alternate combustion air opening (upflow or horizontal)
- Alternate vent/flue location (upflow or horizontal left)
- Annual inspection checklist
- Auxiliary limit control (location and purpose)
- Auxiliary limit switch open (blower compartment)
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Source: Goodman GMVC96 Service and Troubleshooting, p. 61. Written in our own words; check the manual for your exact model.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.