Fujitsu Mini Split Error Code 40: How to Fix It

Q: What does error code 40 mean on a Fujitsu mini split?

Error code 40 indicates a fault with the outdoor unit's heat exchanger thermistor. This sensor measures the temperature of the outdoor coil, and the system shuts down to prevent damage.

Q: Can I run my Fujitsu mini split with error 40?

No, the system will not operate normally. You should not bypass the error; instead, troubleshoot and fix the issue to prevent further damage.

Q: How much does it cost to fix a Fujitsu error 40?

If you replace the thermistor yourself, the part cost is around $15-$40. Professional service can cost $100-$200 for diagnosis plus part and labor. Board replacement can be more expensive.

Q: Can a dirty outdoor coil cause error code 40?

While a dirty coil can cause performance issues, error 40 is specifically a thermistor or wiring fault. However, cleaning the coil may help if the sensor is physically obstructed or its mounting is compromised.

Q: Where is the thermistor located on my Fujitsu outdoor unit?

It is typically located on the outdoor coil (the large finned heat exchanger), near the refrigerant line connections. It is a small, plastic-tipped sensor with two wires.

Abstract

Error code 40 on your Fujitsu mini-split indicates a fault with the outdoor unit's heat exchanger thermistor. This sensor monitors the temperature of the outdoor coil, and the system halts to prevent damage. The issue is often a faulty thermistor, a wiring problem, or a circuit board fault. This guide will help you diagnose and fix the problem.