Lennox SLP98UHV Error Code A: Indoor Blower CFM Setting
What Does Code A Mean?
The letter A in the SureLight control's menu is the indoor blower CFM (cubic feet per minute) readout. It appears when someone presses and cycles the diagnostic push button on the control board, and the LED alternates between the letter A and the current airflow value, roughly one second on and half a second off.
This is a technician's readout rather than a fault. On a modulating furnace like the SLP98UHV, airflow is matched to the firing rate to keep the temperature rise across the heat exchanger correct, so the board stores separate CFM settings for heating, cooling, and continuous fan. The A item lets an installer confirm the blower is moving the intended amount of air through your ductwork.
No action is required. Once the diagnostic menu times out, the display leaves the A item and returns to normal operation or the idle decimal. If you did not press the diagnostic button, someone else may have accessed the menu or the button may be sticking.
What You'll Notice
- The 7-segment LED shows the letter A alternating with a multi-digit number (the CFM value), about one second on and half a second off.
- The furnace keeps doing whatever it was doing — heating, cooling, or idle — while the A readout cycles, with no change to airflow or comfort.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Diagnostic push button pressed to view blower CFM settings | Most common | — |
How This Is Diagnosed
Confirm this is a readout and not a fault by noting it only shows while the diagnostic push button is being cycled. Stop pressing the button and let the menu time out — each item advances every five seconds — and the display will move past the A entry back to the normal operating or idle indication, showing nothing is wrong.
- You suspect the blower CFM is set too high or too low for your duct system and comfort is affected
- The airflow numbers do not match what was specified for your home during installation
Frequently Asked Questions
What does the letter A mean on my Lennox SLP98UHV?
A is the diagnostic readout for the indoor blower's airflow in cubic feet per minute (CFM). It is information a technician pulls up with the diagnostic button, not an error.
Did I break something by pressing the diagnostic button?
No. Cycling the diagnostic menu only displays settings; it does not change how the furnace runs. The A readout clears on its own once the menu times out.
Why does the CFM number differ between modes?
The SLP98UHV uses different blower speeds for heating, cooling, and continuous fan, so the CFM value shown depends on which mode's setting is being displayed.
✓ Verified against manufacturer service manual — March 2026