HVACopediaGoodman · Furnace troubleshooting
Check and adjust temperature rise
What is going on
Temperature rise depends on airflow and firing rate. An incorrect rise can cause condensing or overheating of the heat exchanger.
Likely causes
- Too little airflow raises temperature rise. Too much airflow lowers it.
Check in this order
- Run the furnace with burners firing for about 10 minutes. Do not exceed the nameplate input.
- Make sure all registers are open and duct dampers are in their final positions.
- Place thermometers in the supply and return ducts as close to the furnace as possible, out of direct view of the heat exchanger.
- Allow readings to stabilize, then subtract return air temperature from supply air temperature.
- To reduce temperature rise, increase blower speed. To increase temperature rise, decrease blower speed. See the Circulator Blower Speed section for speed changes.
- Measure motor current draw to confirm the motor is not overloaded.
Applies to: Gas furnaces ACVC96/AMVC96/GCVC96/GMVC96
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 manual, p. 47. 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.