Coleman air conditioner shows E5 and will not start or stops shortly after starting; may indicate communication issues between indoor and outdoor units.

Safety: Turn OFF power to both indoor and outdoor units at their breakers and disconnects before touching any wiring.

• Verify thermostat wiring: Remove the thermostat cover. Confirm R, C, Y, G, and O/B (if heat pump) are correctly landed per the Coleman wiring diagram. Look for loose or shorted conductors.
• Inspect low-voltage cable: At the air handler and condenser, open the control compartments. Check the 24V control wires (often brown jacketed cable) for cuts, rodent damage, or splices that may be loose or corroded.
• Tighten connections: Reseat and tighten all low-voltage terminal screws on the Coleman control boards and contactor coil terminals. Ensure no bare wires are touching each other.
• Check for correct polarity: Some Coleman systems require correct line voltage polarity and a solid equipment ground for communication. Verify hot, neutral, and ground are correctly wired at the disconnect and service panel.
• Power cycle: After correcting any wiring issues, restore power to indoor and outdoor units. Wait 5–10 minutes for boards to boot and attempt communication. Clear the E5 by cycling thermostat power.
• Board diagnosis: If E5 persists and wiring is confirmed good, one of the control boards may be defective. A technician can test 24V signals and board LEDs to determine whether the indoor or outdoor Coleman board has failed.

Note: Never connect or disconnect low-voltage wires with power on; you can damage the boards.