American Standard HVAC Manuals

Most Common Diagnostic Codes (Communicating Systems – ComfortLink II)

• Hard Lockout / 2 Flash / System Lockout: Ignition failure after retries – check flame sensor (clean with steel wool); verify gas pressure (3.5" WC natural); inspect ignitor & ground.
• Comm Failure / No Communication: Lost link between thermostat, indoor & outdoor units – check 4-wire bus (R, B, D+, D-); confirm polarity & no shorts; power cycle all components.
• High Limit Open / 4 Flash: Furnace rollout or limit switch open – check for restricted airflow, dirty filter, blocked vents; reset limit switch; may indicate heat exchanger issue.
• Pressure Switch Open / 1 Flash: Inducer motor not proving draft – check vent pipe for blockage; inspect pressure switch tubing & hoses; verify inducer spins freely.
• Low Flame Sense / 7 Flash: Weak flame detection – clean flame sensor; check burner alignment & gas orifice; verify proper manifold pressure.
• Outdoor Unit Fault / AC/HP Codes: High pressure / low pressure switch open – check refrigerant charge, dirty coils, fan operation; possible TXV or expansion valve issue.

Variable Speed / Platinum / Gold Series Specific (2020–2026)

• Variable Speed Blower Fault: ECM motor communication or power issue – check 24V to motor module; inspect harness; may need motor replacement.
• Refrigerant Pressure Fault: High/Low pressure – clean condenser/evaporator coils; check filter drier & charge level (professional required).
• Defrost Fault (Heat Pump): Stuck in defrost or failure to terminate – check defrost board, sensor, & reversing valve; verify outdoor fan runs.

General HVAC Specific

• No Heat / No Cool: Check thermostat settings & batteries; verify breaker/fuse; ensure disconnect at outdoor unit is ON; check air filter.
• Short Cycling: Dirty filter/coils, low refrigerant, oversized unit, or thermostat placement issue – replace filter; schedule professional service for charge check.
• Uneven Temperatures: Blocked vents/registers; check zoning dampers if equipped; verify blower speed settings.
• Noisy Operation: Loose panels, failing blower motor bearings, or debris in blower wheel – tighten screws; clean or lubricate (professional recommended).

Safety note: HVAC systems involve high voltage (120/240V), gas, and refrigerant under pressure. Always turn off power/gas at disconnect and breaker before servicing. Never bypass safety switches or limits. Refrigerant handling requires EPA certification. For gas leaks, electrical faults, or refrigerant issues, contact a licensed HVAC professional immediately.