What happens
The intended return conductor on equipment that requires a neutral is interrupted.
Typical symptoms
Erratic controls, abnormal line-to-neutral readings or intermittent indoor equipment power.
Checks that distinguish this cause
Qualified personnel evaluate the actual supply arrangement and compare measurements across the intended conductors. Inspect isolated neutral connections along the branch.
What can look similar
Not all HVAC supplies use a neutral. Ground-referenced voltage is not proof of a healthy neutral.
Repair direction
Restore the specified neutral path and grounding arrangement; do not use cabinet ground as a return.
Verify the repair
Verify stable line-to-neutral supply while the connected equipment operates.
Equipment-specific limits
Protective earth is not a substitute for neutral. An open neutral must not be repaired by adding a neutral-to-chassis bond at equipment.
Practice this diagnosis
These simulated calls exercise this component or repair family. The article describes a broader diagnostic process; a call may represent a different cause within that family.
References and applicability
Original HVACSim explanations with manufacturer and instrument-maker references for further reading. These resources support the subject; their model-specific examples are not specifications for every system.
- Fluke: HVAC and industrial electrical testing applicationsElectrical measurement principles, including control-circuit voltage references.
- Copeland: Compressor terminal venting safetyStop conditions and hazards around compressor electrical terminals.
Editorial review: 2026-09-29. Verify the current manual for the installed model.