What It Means
Implausible temperature relationship detected between outdoor air and coil thermistors.
Bryant Heat Pump
Bryant Heat Pump Error Code 56
Troubleshooting guide for the Bryant Heat Pump system fault 56.
Possible Causes
- Out-of-calibration outdoor air or outdoor coil thermistor.
- Swapped or crossed sensor wiring harness connectors.
- Poor sensor thermal contact at coil mounting location.
Not sure which one it is — or if it's none of these? Try ACLogics today.
Disclaimer: This information is for general reference. Error codes can vary by model and production year. Always refer to your machine's specific manual and the information printed on the unit itself.
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Full Diagnosis
OAT-OCT Thermistor Out of Range. The board cross-checks the outdoor air temperature sensor against the outdoor coil temperature sensor and finds their combined reading implausible without being able to determine from that comparison alone which single sensor is at fault. Because both readings feed defrost logic (comparing coil temperature to outdoor air temperature is how the board decides when frost has accumulated and defrost is needed), the unit loses reliable defrost timing until the fault is resolved, which in cold-weather heating operation can lead to a frosted-over outdoor coil if left unaddressed. This differs from code 53 (Outdoor Air Temp Sensor Fault) and code 55 (Coil Temp Sensor Fault), both single-sensor faults triggered when one specific sensor reads outside its own valid resistance range in isolation — 56 instead fires on the relationship between two otherwise in-range-looking readings. When 56 appears without 53 or 55 also present, both sensors need to be checked individually since neither has tripped its own fault threshold.
All Recorded Causes
Ohm out both the outdoor coil sensor and the outdoor air temperature sensor against their respective temperature/resistance charts at their actual current temperatures — since this is a comparison fault, both need checking even though neither may show as individually out of range. Check all sensor wiring for shorts, crossed connections, or a swapped harness connector between the two sensors, a common way to produce a plausible-looking but wrong comparison. Verify both sensors are properly seated and making good thermal contact with their respective locations. Replace whichever sensor is confirmed out of specification once both have been individually checked; if both check out individually, suspect a wiring cross-connection rather than either sensor.
Verify Before Replacing Parts
- Confirm the exact Bryant model family and heat pumps context before acting on a generic code description.
- Confirm filter condition, blower operation, and coil cleanliness before replacing any controls — start by ruling out whether ohm out both the outdoor coil sensor and the outdoor air temperature sensor against their….
- Measure airflow-related readings that match the symptom, such as temperature split or static pressure, and check whether check all sensor wiring for shorts, crossed connections, or a swapped harness connector be….
- After the correction, run the system long enough to confirm the heat pumps fault does not return under normal load.
Still unsure about this fault?
ACLogics walks you through Bryant Heat Pump diagnostics step-by-step — so you confirm the cause before swapping parts.
