Trane air conditioner displays E7 and the outdoor unit does not start; thermostat may show a communication or outdoor unit error.

Safety first: Turn off power before removing any covers. Use a non-contact voltage tester to verify power is off.

• Check power supply: Verify the outdoor unit breaker is ON and the disconnect fuses (if present) are intact. Replace blown fuses only after determining the cause.
• Inspect low-voltage fuse: On the indoor Trane control board, locate the low-voltage blade fuse (often 3–5A). If blown, replace with the same rating. A short in thermostat or outdoor wiring can cause repeated failures.
• Check cable continuity: Inspect the thermostat cable from indoor to outdoor unit for cuts or crushed sections. Repair or replace as needed.
• Board LED status: With power restored, check the outdoor control board status LED (if equipped). No LED or erratic flashing may indicate a failed board.

If the outdoor unit remains offline after restoring power and low-voltage circuits, a Trane technician should test the control board and compressor contactor circuit.