HVACopediaAllied · Furnace troubleshooting
Check temperature rise and adjust blower speed
What is going on
Temp rise check on the Allied. Run it until supply and return temps settle, then measure. Out of range means a speed change.
Likely causes
- Temperature rise outside the nameplate range can cause erratic limit operation
- Blower speed set too low, giving a high rise
- Dirty filter or restricted ductwork
Check in this order
- Run the furnace until supply and return air temperatures stabilize.
- Measure the temperature rise, supply minus return.
- Compare it to the range on the unit nameplate.
- If it is outside the range, change the blower speed.
- Raise blower speed to lower the temperature rise.
- Lower blower speed to raise the temperature rise.
- Recheck the temperature rise after each change.
Applies to: Heating airflow adjustment
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Source: Allied 92G1UH installation instructions manual, p. 46. 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.