Lennox SLP98UHV Error Code E 348: No 24V Output Y2 to C
What Does Code E 348 Mean?
Error code E348 on the Lennox SLP98UHV indicates that there is no 24-volt output between the Y2 and C terminals with a non-communicating outdoor unit. The Y2 relay (Stage 2 cooling relay) on the control board has failed — the relay contacts did not close or the relay coil did not energize.
The Y2 signal activates the second stage of cooling on two-stage air conditioners or heat pumps. Without this signal, the system is limited to first-stage cooling only (if Y1 is working). You may notice that the air conditioner runs but cannot keep up with cooling demand on hot days, because it cannot reach full capacity.
Like E347, this is an internal control board relay failure that requires board replacement. A technician should verify the fault by testing for 24V at the Y2 terminal during a second-stage cooling call, and replace the board if confirmed.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Y2 relay on control board has failed | Most common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Your air conditioner runs but cannot maintain the set temperature on warm days
- You have a two-stage system and only one stage of cooling seems to work
- Both E347 and E348 appear, suggesting multiple relay failures on the control board
✓ Verified against manufacturer service manual — March 2026