Carrier · Status code
Carrier 59TN7A status code 51: outdoor-air temperature sensor open or short
Major code 51 reports the outdoor-air temperature (OAT) sensor circuit used by the communicating system. Minor 51.1 means the sensor reads open; minor 51.2 means it reads shorted.
On the control
- Code
- 51
- Minor
- 51.1 · 51.2
- Door LED
- 5 short flashes then 1 long
- Controller
- 59TN7A integrated furnace control with 3-digit LCD display and door LED
- Applies to
- Carrier Infinity 97 (59TN7A)
- Manual
- 59TN7A-01SI
What each minor code says, verbatim
| Display | Manufacturer wording |
|---|---|
| 51.1 | OAT - Open |
| 51.2 | OAT - Short |
A code is a condition, not a diagnosis
Open or short readings come from the sensor, its wiring or its connector. The circuit is tested with the sensor disconnected and its resistance checked against the accessory specification.
Which furnaces this applies to
Documented for Carrier 59TN7A Infinity 97 furnaces in installation instructions 59TN7A-01SI, Fig. 61 service label. The OAT sensor is part of the outdoor unit or system configuration.
Scope: Carrier 59TN7A Infinity 97 furnaces with the on-board 3-digit display control. Not sure which control you have? Send us the full model number from the rating plate.
Safe things to look at first
- Read the full code on the control display through the door, including any minor digit (for example 33.2), and write it down.
- Look, without touching, for obvious conditions you can report: snow or ice at the vent terminations, water on the floor, a loaded filter, a condensate pump that is full or off.
- Note whether the furnace still heats at all, and how long it runs before the code returns.
- Note whether the furnace still heats normally; a sensor fault alone does not stop the burner.
Do not
- Do not bypass or jumper the door switch, limit switches, rollout switches or pressure switches.
- Do not open the burner compartment, disconnect tubing, or adjust the gas valve or gas pressure.
- Do not keep cycling power to force the furnace to relight; repeated resets hide the fault and can allow unburned gas to build up after ignition failures. If the code returns, stop and call.
What a technician does
- A technician checks the sensor wiring and connector and replaces the sensor only if it fails a resistance test.
Questions people ask
Where is the OAT sensor on my system?
The outdoor-air temperature sensor belongs to the outdoor (heat pump or air conditioner) side of an Infinity system. The furnace reports its circuit here; the technician checks the outdoor connections.
Seeing code 51 on your Carrier?
Tell us the full code, the model number and whether the furnace still heats on low. BC Wide prioritizes no-heat calls across Greater Vancouver.