Carrier 59SC5A Error Code 23: Pressure Switch Did Not Open
What Does Code 23 Mean?
Status code 23 on the Carrier 59SC5A means the pressure switch did not return to its open (default) position when the control board expected it to. Pressure switches are normally-open safety devices that close only when the inducer motor creates proper draft. Once the inducer stops, the switch should open back up.
The most common cause is an obstruction in the pressure tubing — the narrow hose connecting the pressure switch to the inducer housing or collector box. Condensation, insect nests, or accumulated debris can block this tubing and maintain pressure on the switch diaphragm even after the inducer is off. The switch itself can also develop stuck contacts, particularly in older furnaces where the internal mechanism has worn.
A technician needs to inspect the pressure tubing for obstructions, blow it clear if necessary, and test the pressure switch to verify it opens and closes at the correct pressure values. If the switch contacts are mechanically stuck, the switch must be replaced.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Obstructed pressure tubing | Common | ✗ Call a pro → |
| Pressure switch stuck closed | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- When this code appears — pressure switch testing and tubing inspection require professional HVAC service
✓ Verified against manufacturer service manual — March 2026