What happens
A failed coil cannot generate the magnetic force needed to pull in the contactor.
Typical symptoms
Outdoor unit silent despite a valid call at the coil.
Checks that distinguish this cause
Confirm the specified voltage across the actual coil terminals during demand. With safe isolation and the coil disconnected, compare resistance with its specification.
What can look similar
Missing common, a safety interruption or low control voltage can prevent pickup with a healthy coil.
Repair direction
Fit the correctly rated contactor after ruling out supply and downstream faults.
Verify the repair
Verify clean pickup and release and power delivery through each required pole.
Equipment-specific limits
Coil voltage and contact arrangement vary. A click proves movement, not that every power pole conducts correctly.
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.
- Fluke: HVAC multimeter troubleshooting guideIntroductory meter applications. Actual equipment ratings take precedence over generic examples.
Editorial review: 2026-09-29. Verify the current manual for the installed model.