Thermostat displays E2 and cooling or heating from the outdoor unit is disabled

Safety warning: Turn off power to the outdoor condenser/heat pump at the disconnect and breaker before opening the panel.

• Step 1 – Verify outdoor power: Check the outdoor unit breaker and the disconnect near the unit. Reset if tripped. If it trips again, stop and call a technician.
• Step 2 – Inspect outdoor communication wiring: Remove the service panel on the outdoor unit and locate the low-voltage/communication terminals. Confirm the communication wires from the thermostat/indoor unit are tight and not pinched or shorted to the cabinet.
• Step 3 – Check cable condition: Follow the low-voltage cable from the house to the outdoor unit. Look for cuts, UV damage, or animal chewing. Repair or replace damaged cable.
• Step 4 – Confirm correct polarity: For ComfortLink II systems, ensure the communication wires are landed on matching terminals (e.g., A to A, B to B) at thermostat, indoor, and outdoor boards.
• Step 5 – Power cycle: Restore power to the outdoor unit and indoor unit, then wait 5–10 minutes for the system to re-establish communication.
• Step 6 – If E2 persists: The outdoor control board or thermostat may be defective. Further diagnosis with a meter and Trane service literature is required.