42 - Indoor unit heat exchanger middle temperature sensor error.
Fujitsu General's official table labels code 42 as an indoor unit heat exchanger middle temperature sensor error.
Family context is taken from Fujitsu General's floor-mounted split-system product pages. Error-code mappings below are conservatively taken from an official Fujitsu General installation-manual error table for a floor-mounted indoor unit, so exact display behavior and applicability can vary by controller and connected system type.
Severity
High
Display
Presented in the official error table as an indoor-unit error indication during operation.
Support first?
Often not
Models in range
AGU9RLF, AGU12RLF, AGU15RLF
What to do first
Start with these checks
- 1Record the code and avoid repeated restart attempts
- 2Restart the unit once to see whether the fault clears
- 3Request service if the code remains or heating/cooling performance is abnormal
Likely causes
What usually sits behind this code
Indoor heat-exchanger temperature sensor fault
Sensor harness or connector issue
Control board cannot read the heat-exchanger sensor correctly
Contact support
Contact customer support if any of these apply
- !The code persists after restart
- !Air temperature or system cycling becomes abnormal
- !The unit stops operating shortly after startup
- - The official description is brief, so the cause list here stays conservative.
- - This is a sensor-related service fault rather than a routine cleaning reminder.
Related codes
Nearby codes in this family
Source notes
Source and scope
Source: Fujitsu General installation manual
Official error-code table snippet for a Fujitsu General floor-mounted indoor unit lists code 42 as Indoor unit heat ex. middle temp. sensor error.
Last reviewed: 2026-04-19
Use this as an official-first pointer, not a repair authorization. Exact troubleshooting steps and code visibility vary by model, controller, and system configuration.