Lennox SLP98UHV Error Code C: Cooling Stage Display
What Does Code C Mean?
The letter C on the Lennox SLP98UHV display indicates the cooling stage diagnostic readout. This appears when cycling through the diagnostic menu using the push button on the control board. The display shows the cooling stage number (1 or 2) followed by the CFM setting for that stage.
This is purely informational and indicates that the diagnostic menu has been accessed. The SLP98UHV supports two-stage cooling when paired with a compatible air conditioner or heat pump. Stage 1 is the lower-capacity mode used for moderate cooling needs, and Stage 2 is full capacity for hot days. Each stage has its own blower speed setting to match the airflow to the cooling output.
No action is needed. The display will cycle through other diagnostic items or return to idle on its own. This readout is used by technicians to verify the cooling configuration matches the outdoor unit installed with the furnace.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Diagnostic push button pressed to view cooling stage settings | Most common | — |
When to Call a Professional
Contact a licensed HVAC technician if:
- You believe the cooling stages or airflow are not configured correctly for your system
✓ Verified against manufacturer service manual — March 2026