Lennox air conditioner does not respond to thermostat; control board indicates E202 communication fault between indoor and outdoor units (common on communicating Lennox systems with iComfort thermostats).

Safety: Shut off power to both indoor and outdoor units at the breakers before accessing control compartments.

• 1. Verify wiring polarity: Communicating Lennox systems use specific terminals (e.g., i+, i−, C). Confirm the same color wire goes to the same terminal at thermostat, indoor unit, and outdoor unit. Reversed polarity will cause E202.
• 2. Tighten all communication terminals: At the indoor control board and outdoor control board, gently tug each communication wire. Retighten any loose screws and ensure no bare copper is touching adjacent terminals.
• 3. Inspect cable for damage: Follow the communication cable run between indoor and outdoor units. Look for rodent damage, UV cracking, or splices exposed to moisture. Replace any damaged sections with proper thermostat/communication cable.
• 4. Power cycle the system: Turn off both breakers for 5 minutes, then restore power to the indoor unit first, then the outdoor unit, then the thermostat. Allow several minutes for the devices to re-establish communication.

When to call a technician: If wiring is correct and intact but E202 persists, the outdoor or indoor control board may be defective and should be tested and replaced by a Lennox-trained technician.