Thermostat shows E2 and may indicate 'Outdoor sensor error' or 'Outdoor temp unavailable'.

Safety first: Turn off power to both indoor and outdoor units at the service disconnects and breakers.

Diagnostic steps:

• Locate the outdoor sensor: On many Rheem systems, the outdoor temperature sensor is mounted near the outdoor condenser coil and wired back to the indoor control board or communicating bus.
• Inspect wiring: Check the sensor leads for cuts, abrasions, or UV damage. Ensure the sensor wires are firmly attached to the designated outdoor sensor terminals.
• Check resistance: Disconnect the sensor from the board and measure its resistance with a multimeter. Compare the reading to Rheem's temperature/resistance chart (typically a 10k or 20k NTC thermistor). An open (infinite) or near-zero ohm reading indicates a failed sensor.
• Verify connections at the board: Ensure the sensor wires are not landed on the wrong terminals and that there are no loose screws or corrosion.
• Replace if defective: If the sensor tests bad, install a new Rheem-compatible outdoor temperature sensor, route the cable away from high-voltage lines, and secure it.
• Restore power: Turn power back on and allow several minutes for the thermostat to recognize the sensor and clear the E2 code.