Thermostat shows E3 and will not control cooling properly, outdoor temperature not available

Safety first: Turn off power to the furnace/air handler and outdoor unit at the breaker before touching any wiring.

• Step 1 – Confirm system uses an outdoor sensor: Not all Amana smart thermostat installations include an outdoor sensor. If your system never had outdoor temperature displayed, E3 may indicate a configuration issue rather than a failed sensor.
• Step 2 – Check thermostat configuration: In the thermostat settings menu, verify that the outdoor sensor option is correctly set (enabled only if a sensor is installed). Disable the sensor option if none is installed and see if E3 clears.
• Step 3 – Inspect wiring at the furnace/air handler: Locate the low-voltage control board on the Amana furnace or air handler. Find the terminals labeled for outdoor sensor (often S1/S2 or OT/OT). Ensure the sensor wires are firmly attached and not broken.
• Step 4 – Inspect outdoor sensor: Find the Amana outdoor temperature sensor near the condenser or on an exterior wall. Check for physical damage to the sensor body or cable. Repair any obvious cuts or breaks in the cable using appropriate low-voltage splices, or replace the sensor if damaged.
• Step 5 – Test sensor resistance (advanced): With power off, disconnect the sensor leads and measure resistance with a multimeter. Compare to Amana’s sensor resistance chart (typically a thermistor). An infinite reading indicates an open sensor that must be replaced.
• Step 6 – Replace sensor: If the sensor is open or damaged, install a new Amana-compatible outdoor temperature sensor and reconnect to the control board terminals. Restore power and verify E3 is cleared.

When to call a professional: If you cannot locate the sensor wiring or are unsure of the correct terminals, contact an HVAC technician familiar with Amana systems.