Thermostat displays E4 and may shut down heating or cooling, outdoor temperature reading is incorrect or missing

Safety first: Turn off power to both indoor and outdoor units at the breaker before working on wiring or sensors.

• Step 1 – Power reset: Turn off the HVAC breakers for 2–3 minutes, then restore power. If E4 returns immediately, proceed with inspection.
• Step 2 – Inspect outdoor sensor cable: Trace the sensor cable from the Amana outdoor temperature sensor back to the furnace/air handler. Look for crushed, pinched, or chewed sections. Repair or replace damaged cable.
• Step 3 – Check sensor housing: Examine the sensor body for cracks or water intrusion. If the sensor is wet inside or corroded, it is likely shorted and must be replaced.
• Step 4 – Test resistance: With power off, disconnect the sensor leads at the control board. Measure resistance across the sensor. A near-zero ohm reading indicates a shorted sensor. Replace with a new Amana-compatible outdoor sensor.
• Step 5 – Inspect control board terminals: If a known-good sensor still reads as shorted when connected, the sensor input on the Amana control board may be damaged. This requires board replacement by a professional.

When to call a professional: If you suspect a failed control board or cannot safely access the furnace/air handler compartment, contact an HVAC technician.