Carrier 25HNA6 / 25HNA9 Heat Pump Codes

Applies to: Carrier 25HNA6 / 25HNA9 (Infinity two-stage heat pump, Puron). Amber STATUS light on the outdoor control board, two-digit status codes.

Several codes apply to only one of the two models (25HNA6 or 25HNA9); those rows say which. The newer 25HNB6 / 25HNB9 has a shorter list and its own chart.

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 open.	Low-pressure switch trip. 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 (25HNA9 only).	Compressor voltage not sensed when the compressor should be starting. Contactor may be stuck open, or there is a wiring error. How to fix →
75	Low stage did not start (25HNA6 only).	Specified start voltage at the VR terminal was not achieved in low stage. Start relay was de-energized after 1 second. How to fix →
76	Low stage did not start 3 times (25HNA6 only).	For 3 consecutive low stage starts, the specified start voltage at the VR terminal was not achieved and the start relay was de-energized. Low stage is locked out for 30 minutes. How to fix →
77	High stage did not start (25HNA6 only).	Specified start voltage at the VS terminal was not achieved in high stage. Start relay was de-energized after 1 second. How to fix →
78	High stage did not start 3 times (25HNA6 only).	For 3 consecutive high stage starts, the specified start voltage at the VS terminal was not achieved and the start relay was de-energized. High stage is locked out for 30 minutes. How to fix →
81	Low stage thermal lockout.	Thermal cutout in three consecutive low/high stage 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 high/low stage 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 →
85	Low contactor open (25HNA6 only).	Compressor voltage not sensed when the compressor should be starting. Low stage contactor may be stuck open, or there is a wiring error. How to fix →
87	High contactor open (25HNA6 only).	Compressor voltage not sensed when the compressor should be starting. High stage contactor may be stuck open, or there is a wiring error. 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. Rapid continuous flashing (25HNA9 only): emergency mode, running from standard thermostat inputs instead of the Infinity Control, high stage only.
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 25HNA Infinity Series Heat Pump Installation Instructions, 25HNA-5SI, Table 6 Troubleshooting, p. 14. 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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Carrier 25HNA6 / 25HNA9 Heat Pump Codes

How to read the codes

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