Armstrong Air communicating thermostat displays E2; system may operate erratically.

Steps to check:

• Locate outdoor sensor: Find the Armstrong Air outdoor temperature sensor mounted near the outdoor unit or on an exterior wall.
• Inspect wiring: Check for cuts, abrasions, or loose connections at the sensor and furnace/thermostat terminals.
• Test sensor resistance: With power off, disconnect the sensor and measure its resistance. Compare to the temperature/resistance chart in the Armstrong Air service manual. If readings are far off, replace the sensor.
• Replace sensor: Install a new Armstrong-compatible outdoor sensor and secure wiring against weather and mechanical damage.