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Carrier 25HNB6 / 25HNB9 Heat Pump Codes
Other Carrier and Bryant two-stage outdoor units use similar two-digit status codes, but the list varies by model and board. Check the unit's own installation instructions.
| Code | Meaning | What to check |
|---|---|---|
| 16 | System communications failure. | Communication with the User Interface lost. Check wiring to the User Interface and the indoor and outdoor units. |
| 25 | Invalid model plug. | Control does not detect a model plug or detects an invalid one. The unit will not operate without the correct model plug. |
| 31 | High pressure switch open. | High-pressure switch trip. Check refrigerant charge, outdoor fan operation and coils for airflow restrictions. How to fix → |
| 32 | Low pressure switch or discharge temperature switch open. | Check refrigerant charge and indoor airflow. How to fix → |
| 45 | Control fault. | Outdoor unit control board has failed and needs to be replaced. |
| 46 | Brown out (230 V). | Line voltage below 187 V for at least 4 seconds. Compressor and fan are not allowed until voltage is 190 V or more. Verify line voltage. |
| 47 | No 230 V at unit. | No 230 V at the contactor when the indoor unit is powered and there is a cooling or heating demand. Verify the disconnect is closed and 230 V wiring is connected to the unit. How to fix → |
| 53 | Outdoor air temperature sensor fault. | Sensor not reading or out of range. Ohm out the sensor and check wiring. |
| 55 | Outdoor coil sensor fault. | Sensor not reading or out of range. Ohm out the sensor and check wiring. How to fix → |
| 56 | Thermistors out of range. | Improper relationship between the coil sensor and outdoor air sensor. Ohm out both sensors and check wiring. |
| 71 | Low stage thermal cutout. | Compressor operation detected, then lost, while low stage demand exists. Possible causes: internal compressor overload trip, or start relay and capacitor held in the circuit too long (if installed). How to fix → |
| 72 | High stage thermal cutout. | Compressor operation detected, then lost, while high stage demand exists. Possible causes: internal compressor overload trip, or start relay and capacitor held in the circuit too long (if installed). How to fix → |
| 73 | Contactor shorted. | Compressor voltage sensed with no demand for compressor operation. Contactor may be stuck closed, or there is a wiring error. How to fix → |
| 74 | No 230 V at compressor. | Compressor voltage not sensed when the compressor should be starting. Contactor may be stuck open, or there is a wiring error. How to fix → |
| 81 | Low stage thermal lockout. | Thermal cutout in three consecutive cycles. Low stage is locked out for 4 hours or until 24 V power is recycled. How to fix → |
| 82 | High stage thermal lockout. | Thermal cutout in three consecutive cycles. High stage is locked out for 4 hours or until 24 V power is recycled. How to fix → |
| 83 | Low-pressure lockout. | Low pressure switch trip during 3 consecutive cycles. Unit is locked out for 4 hours or until 24 V power is recycled. How to fix → |
| 84 | High-pressure lockout. | High pressure switch trip during 3 consecutive cycles. Unit is locked out for 4 hours or until 24 V power is recycled. How to fix → |
How to read the codes
- Short flashes are the first digit and long flashes the second. For example, 3 short then 2 long = code 32.
- A short flash is 0.25 seconds on and a long flash 1 second on, with 0.25 seconds between flashes, 1 second between the short and long groups, and 2.5 seconds off before the code repeats.
- On solid with no flash: standby, no call. 1 flash then pause: low stage running. 2 flashes then pause: high stage running. 5 or 6 flashes then pause show the brown-out protection setting (5 disabled, 6 active).
- Codes 31, 32, 71 and 72: the contactor is de-energized and the outdoor fan runs for up to 15 minutes. If demand is still there, the control tries the compressor again after the 15-minute delay, and keeps trying every 15 minutes. Cycling low voltage defeats the delay.
Codes point to a circuit, not a part. Test before replacing anything, and never jumper a pressure switch to keep a unit running. Line-voltage work is for trained technicians, and refrigerant work requires EPA 608 certification.
Source: Carrier 25HNB6 / 25HNB9 Infinity 2-Stage Heat Pump Installation Instructions, 25HNB6-9-4SI, Table 6 Troubleshooting, p. 13. The "meaning" column follows the manufacturer's wording; "what to check" is our field summary. Always go by the label on the unit you're working on.
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