What It Means
Low line voltage feed to outdoor unit.
Rheem AC & Heat Pump
Rheem AC & Heat Pump Error Code 27
Troubleshooting guide for the Rheem AC & Heat Pump system fault 27.
Possible Causes
- Tripped main breaker or outdoor disconnect.
- Blown high-voltage line fuse.
- Loose high-voltage lug connection.
- Utility voltage drop or brownout.
- Pitted contactor contacts.
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
Outdoor unit control has detected supply (line) voltage below the minimum it needs to operate reliably, or no line voltage at all, at a point it expected power to be present. This is the low-voltage counterpart to code 28 (high line voltage) and is a power-supply fault rather than a low-voltage/24V control-circuit issue like code 09 — 27/28 concern the 208/230V feed to the unit, while 09 concerns the thermostat-level control transformer circuit. The control will not run the compressor/outdoor fan while this fault is active to protect the compressor from low-voltage operation.
All Recorded Causes
Open or tripped outdoor disconnect, tripped breaker at the panel, blown fuse, loose or corroded high-voltage lug or wire nut, undersized wire causing excessive voltage drop under load, a brownout or genuine utility supply problem, or a failing contactor not passing full voltage through. Measure voltage directly at the unit's line-voltage terminals under load, not just at the disconnect, to rule out a downstream connection fault.
Verify Before Replacing Parts
- Confirm the exact Rheem model family and ac and heat pump context before acting on a generic code description.
- Verify current draw, overload status, and control signal before condemning the compressor or drive, given that open or tripped outdoor disconnect, tripped breaker at the panel, blown fuse, loose or cor….
- Look for upstream conditions such as airflow or charge issues that may be pushing the compressor into protection, and check measure voltage directly at the unit's line-voltage terminals under load, not just at the….
- After the correction, run the system long enough to confirm the ac and heat pump fault does not return under normal load.
Not sure which system this Rheem code is on?
ACLogics has guided diagnostics for 57 Rheem fault codes and asks the right questions to narrow it down.
