What It Means
Space relative humidity (SPRH) sensor signal below threshold.
Carrier Packaged Unit
Carrier Packaged Unit Error Code 77
Troubleshooting guide for the Carrier Packaged Unit system fault 77.
Possible Causes
- Damaged SPRH sensor wiring or lost 24V power.
- Contaminated or defective humidity sensor element.
- Control misconfigured for uninstalled sensor.
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
Space Relative Humidity Sensor Failure. SPRH input is below threshold while the sensor is configured as installed.
All Recorded Causes
Check SPRH sensor wiring and 24V power supply to sensor. Inspect sensor for damage or contamination. Measure sensor output signal. Replace sensor or reconfigure control to not-installed if sensor is faulty.
Verify Before Replacing Parts
- Confirm the exact Carrier model family and outdoor packaged units context before acting on a generic code description.
- Verify the sensor or thermistor reading against the expected range for the current operating condition, keeping in mind that check SPRH sensor wiring and 24V power supply to sensor.
- Check the sensor harness and board connection before condemning the sensor itself; on Carrier units this is also where you'd confirm inspect sensor for damage or contamination.
- After the correction, run the system long enough to confirm the outdoor packaged units fault does not return under normal load.
Still unsure about this fault?
ACLogics walks you through Carrier Packaged Unit diagnostics step-by-step — so you confirm the cause before swapping parts.
