HVACopediaGoodman · Furnace troubleshooting
Alternate combustion air opening (upflow or horizontal)
What is going on
When the alternate vent location is used (horizontal left side down, or downvent vertical), an alternate combustion air opening can be used. The locating dimple is on the right side of the cabinet, 1 7/8 in. from the front edge, in line with the knockout. The idea is to move the air inlet to match the new vent position so the piping lines up.
Likely causes
- Horizontal left side down installation
- Downvent vertical installation
- Standard air opening conflicting with the pipe route
- Tight space needing the inlet moved
Check in this order
- Remove the screws and combustion air flange from the cabinet.
- Insert the cabinet plug in the unused combustion air hole so it is sealed.
- Drill a pilot hole at the cabinet dimple, sized for the knockout tool.
- Use a knockout tool to make a 3 in. diameter hole, then deburr the edge.
- Install the combustion air flange and secure it with the screws from the first step.
- Reinstall the flange screws to secure the flange to the cabinet.
- Check that the flange is sealed with no air leaks.
Applies to: Upflow and horizontal models using alternate venting
More furnace guides
- Airflow lower than demanded, furnace runs on low stage when high stage is expected
- Alternate vent/flue location (upflow or horizontal left)
- Annual inspection checklist
- Auxiliary limit control (location and purpose)
- Auxiliary limit switch open (blower compartment)
- Blower motor does not have enough information, fails to start 40 consecutive times
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Source: Goodman GMVC96 service and troubleshooting manual, p. 15. 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.