Controls · COMPONENT REFERENCE

Second-stage control and compressor modulation troubleshooting

Coordinates thermostat demand, board outputs, compressor modulation and matching airflow on applicable staged systems.

Failure causes

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

Missing Y2 or incorrect stage configuration →The full-capacity request is absent because of settings, a conductor fault or controller logic.Failed modulation solenoid or connection →A documented solenoid circuit fails to actuate the compressor's stage mechanism.

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.

Copeland: Two-stage scroll compressorsLow-voltage solenoid modulation on applicable two-stage scroll models.
Resideo: RTH6360 thermostat installation and setupExamples of heat-pump O/B and staging setup. Menu numbers vary by thermostat.

Editorial review: 2026-09-29. Verify the current manual for the installed model.