Indoor unit displays E5 and outdoor unit does not start or shuts down; may occur at startup

Safety: Turn off power to both indoor air handler and outdoor condenser at their breakers/disconnects.

Steps:

• Verify wiring diagram: Refer to the Comfortmaker wiring diagram on the unit panel. Confirm correct terminals (e.g., C, Y, R, COM, DATA) between indoor and outdoor units.
• Inspect communication cable: Follow the low-voltage cable between indoor and outdoor units. Look for splices, damage, or rodent chewing. Repair or replace damaged cable with the same gauge and type.
• Check terminal connections: Tighten all low-voltage screws at both units. Ensure no bare wires are touching adjacent terminals.
• Confirm polarity: If the system uses polarity-sensitive communication (e.g., + and -), make sure the same color wire is on the same terminal at both ends.
• Eliminate noise sources: Avoid running communication cable parallel and close to high-voltage lines. If necessary, reroute or shield the cable.
• Power cycle: After corrections, restore power to indoor first, then outdoor. Wait several minutes for boards to sync and check if E5 clears.

Call a technician if: Wiring is correct and intact but E5 persists, indicating a possible failed indoor or outdoor control board.