Thermostat or control module shows E3 and the outdoor unit will not start

Safety first: Shut off power to the outdoor unit at the disconnect before removing any panels.

• Locate the ambient sensor: On many American Standard condensers, the outdoor temperature sensor is a small probe or capsule mounted near the coil or control compartment, connected by two low-voltage wires.
• Inspect wiring and connector: Check for broken, chewed, or sun-damaged wires. Ensure the plug is fully seated on the control board. Clean light corrosion with electrical contact cleaner and a soft brush.
• Check sensor placement: Make sure the sensor is not touching hot discharge lines or in direct sunlight, which can cause false readings. Reposition it in free air near the coil if necessary.
• Replace sensor if damaged: If the sensor body is cracked or the wires are broken at the sensor, replace it with an OEM American Standard outdoor temperature sensor matched to your model.
• If E3 persists: The outdoor control board may be misreading the sensor. Further diagnosis with resistance measurements and board testing should be done by a technician.