Unit attempts to start but quickly stops and displays E5; sometimes accompanied by humming from outdoor unit.

Safety first: Isolate power at the breaker. Do not touch compressor terminals without confirming power is off and discharged.

Steps to try:

• Inspect wiring: Remove the outdoor panel and check compressor terminals and wiring harness for burn marks, melted insulation, or loose lugs. Tighten loose connections and replace burnt wires.
• Check capacitor (non-inverter): If your Tristar model uses a start/run capacitor, visually inspect it. A bulged or leaking capacitor must be replaced with the same µF and voltage rating.
• Check for mechanical seizure: If the compressor hums loudly then trips, it may be seized. Do not repeatedly restart; this can cause further damage.
• Allow cool-down: Let the unit sit powered off for 30–60 minutes to cool the compressor, then try again once.

When to call a technician: Persistent E5 indicates a serious compressor or inverter module issue. A licensed technician should measure compressor winding resistance, insulation, and current draw, and determine if the compressor or inverter PCB must be replaced.