Indoor unit displays E1 and cooling stops intermittently

Safety first: Turn OFF the AC at the breaker and disconnect power before removing any covers. Capacitors can hold charge; do not touch board components directly.

• Step 1 – Power reset: Turn the system OFF at the thermostat/remote, then switch OFF the breaker for 5 minutes. Restore power and check if E1 clears.
• Step 2 – Check communication cable: Remove the indoor unit front panel and access the terminal block. Verify the communication terminals (often labeled 1–2–3 or S1–S2–S3 on Carrier systems) are tight and wires are not burnt or corroded. Tighten any loose screws.
• Step 3 – Inspect outdoor connections: At the outdoor unit, remove the control panel cover. Confirm the same communication wires are landed on the correct terminals and are secure. Look for rodent damage or cuts in the cable between units.
• Step 4 – Check polarity and matching: Ensure wire colors match terminal numbers between indoor and outdoor units. Incorrect polarity can cause E1.
• Step 5 – If fault persists: The indoor or outdoor control PCB may be defective. At this point, contact a qualified Carrier technician to test voltages and replace the faulty board.