Controls · COMPONENT REFERENCE

Indoor fan relay troubleshooting

Switches blower power or a documented blower-enable path when a fan command is present.

Failure causes

Choose a cause for symptoms, checks that separate it from similar faults, repair direction and verification.

Failed relay coil or missing enable →The relay cannot actuate because its coil has failed or the intended command is absent.Open, resistive or welded relay contacts →Contacts fail to pass the required power, or stay closed after the command is removed.

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.