What It Means
Compressor voltage detected without a call for compressor operation.
Carrier Air Conditioner
Carrier Air Conditioner Error Code 73
Troubleshooting guide for the Carrier Air Conditioner system fault 73.
Possible Causes
- Contactor contacts welded closed.
- Faulty contactor coil mechanism.
- Wiring bypass feeding voltage around contactor.
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
Contactor Shorted. The control senses compressor voltage present when there is no call for compressor operation, indicating the contactor contacts are welded closed or there is a wiring fault feeding voltage around the contactor. This is effectively the mirror-image fault to code 74, which flags the opposite condition — no voltage sensed at the compressor when it should be running, typically from a contactor stuck open. It is also distinct from code 47, which reports no 230 V reaching the unit at all from the disconnect, a supply-side problem upstream of the contactor rather than a contact condition. Because the compressor can run whenever line voltage is present regardless of the control signal, a welded contactor risks continuous or unwanted compressor operation and should be treated as an urgent equipment-damage issue rather than a routine no-cool complaint.
All Recorded Causes
Test contactor coil operation and verify it de-energizes fully when the call for cooling ends. Measure contact resistance across the contactor when it should be open — welded contacts will show continuity or voltage downstream when they shouldn't. Inspect for a wiring error that could be feeding compressor voltage around the contactor entirely, independent of contact condition. Replace the contactor if contacts are confirmed welded rather than attempting to free them. Verify wiring is correct and matches the diagram before returning the unit to service, and re-test that voltage disappears at the compressor once the call ends.
Verify Before Replacing Parts
- Confirm the exact Carrier model family and air conditioners 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 test contactor coil operation and verify it de-energizes fully when the call for cooling e….
- Measure airflow-related readings that match the symptom, such as temperature split or static pressure, and check whether measure contact resistance across the contactor when it should be open — welded contacts w….
- After the correction, run the system long enough to confirm the air conditioners fault does not return under normal load.
Still unsure about this fault?
ACLogics walks you through Carrier Air Conditioner diagnostics step-by-step — so you confirm the cause before swapping parts.
