Bryant communicating thermostat shows code 51; indicates outdoor unit capacity or staging error. System may run at wrong capacity or not stage up.

Safety first: Turn off power to the outdoor unit and indoor unit.

Steps:

• 1. Verify model configuration: On the Evolution/Preferred thermostat, confirm that the outdoor unit type (single-stage, two-stage, variable-speed) is correctly configured. Correct any mismatches.
• 2. Inspect staging wiring: At the outdoor unit, check wiring to any staging solenoids or valves (on two-stage scroll compressors or two-stage systems). Ensure connectors are tight and not corroded.
• 3. Check control board settings: Some Bryant boards have dip switches or jumpers for staging. Verify they match the unit's specifications per the installation manual.
• 4. Power cycle and test: Restore power and command different stages from the thermostat (if possible). If the unit fails to change capacity or code 51 persists, the staging solenoid or control board may be defective.

Note: Replacement of staging components and verification of refrigerant charge should be done by a licensed technician.