Ruud air conditioner outdoor unit runs but compressor does not start; control board or diagnostic LED shows E3.

Safety first: Turn off power at the disconnect and verify with a meter. Capacitors can hold a charge; discharge them properly before handling. If you are not experienced with high-voltage circuits, contact a professional.

• Step 1 – Listen for compressor: With the unit powered and calling for cooling, listen: if the fan runs but you hear a brief hum then a click, the compressor may be trying and failing to start.
• Step 2 – Inspect contactor: With power off, remove the control panel cover. Inspect the Ruud contactor for pitted or burned contacts. Manually press the contactor (with power off) to ensure it moves freely. Replace if badly burned or stuck.
• Step 3 – Test start/run capacitor: Locate the dual run capacitor (often labeled C, FAN, HERM). Discharge it by bridging terminals with a resistor or insulated screwdriver. Remove wires (mark their positions) and test capacitance with a multimeter. Replace if more than ±10% out of rating or bulged/leaking.
• Step 4 – Check compressor wiring and terminals: Inspect the compressor terminal cover. Look for burned or loose spade connectors. Repair or replace damaged terminals using proper crimp connectors and high-temperature wire.
• Step 5 – Technician evaluation: If capacitor and contactor are good and wiring is intact, the compressor may be mechanically locked or internally failed. A technician should perform amp draw and megohm tests and replace the compressor if necessary.