Carrier 59SC2B Error Code 12: Blower On After Power Up
What Does Code 12 Mean?
Status code 12 on the Carrier 59SC2B means the furnace blower activated for approximately 90 seconds after power was restored. This occurs when the unit powers up while the thermostat is calling for heat (the R-W circuit is closed) or when the thermostat signal drops during the blower on-delay period.
This is a designed safety behavior, not an error. When power returns during an active heating call, residual heat may be present in the heat exchanger. The blower runs to dissipate this heat safely before the furnace begins a fresh ignition sequence. This protects the heat exchanger and ensures the next heating cycle starts from a safe baseline.
You will typically see this code after a power outage that occurred while your furnace was heating, or after someone manually toggles the furnace power switch during a heating cycle. Once the 90-second purge completes, the furnace returns to normal operation and will respond to the next thermostat call.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Power was restored while thermostat was calling for heat | Most common | — |
- If the blower runs continuously without stopping after the 90-second period — this could indicate a control board or relay issue
✓ Verified against manufacturer service manual — March 2026