Ruud air conditioner shows E5 and may shut down or run with poor cooling performance.

Safety first: Disconnect power at the outdoor disconnect before opening the control panel.

• Step 1 – Locate the ambient sensor: On many Ruud condensers, the outdoor ambient thermistor is mounted near the coil or in the control compartment, connected to the main control board with two small wires.
• Step 2 – Inspect wiring and connector: Check for rodent damage, UV-brittled insulation, or loose plug connections. Reseat the connector on the control board and ensure it is fully engaged.
• Step 3 – Test sensor resistance: With power off, disconnect the thermistor and measure its resistance with a multimeter. Compare to Ruud’s temperature/resistance chart (typically around 10kΩ at 77°F for many NTC sensors). If reading is open, shorted, or far out of range, replace the sensor.
• Step 4 – Clear fault: Restore power and cycle thermostat OFF then ON to clear the error. Monitor operation.
• Step 5 – Board diagnosis: If a known-good sensor still shows E5, the outdoor control board may have a failed sensor input circuit and require replacement.