What happens
Contacts remain mechanically joined after the coil command is removed.
Typical symptoms
Outdoor equipment continues running with the thermostat off.
Checks that distinguish this cause
Determine whether the coil is still energized. If the call is absent but the power poles remain closed, isolate all power and inspect the contactor.
What can look similar
A stuck thermostat signal or short between R and Y keeps a healthy contactor energized.
Repair direction
Replace the damaged contactor and investigate excess current, chatter or cycling.
Verify the repair
Verify the unit stops when demand ends and restarts normally.
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.