Temperature Display (TH21 vs ROOM)

On Fujitsu indoor units, two temperature readings are commonly shown:

• TH21 – The return air sensor temperature inside the indoor unit.
• ROOM – The temperature detected by the wired remote controller or remote sensor. If no sensor or controller, it will read the same as TH21

Understanding these readings is important when comparing on-site values to those shown in the software.

Heating Mode Offset Behavior : When Service Tool is set to display adjusted values or you are using Airstage Cloud.

When a Fujitsu indoor unit has no local wired controller or uses a remote temperature sensor, it references an adjusted temperature for control. This adjustment helps optimize heating performance in commercial environments.

In cooling mode, the ROOM temperature typically matches TH21.
However, when switching to heating mode, the thermistor value is automatically offset to read approximately 7°F cooler than TH21.

This intentional offset allows for improved comfort control but may cause confusion if comparing readings without awareness of the behavior.

Adjusting the Heating Mode Offset

If the temperature offset causes undesirable operation, you can experiment with Function Code 31 (Heat Air Trigger Switch) using either the Service Tool or Airstage Cloud.

 *Either 02 or 01 will be the ones to try.

Procedure (Airstage Cloud):

1. Access the Service Side of the Airstage Cloud.
2. Select the indoor unit you want to adjust.
3. Click Remote Setting.
   ⚠️ This will temporarily shut down the unit. You will need to send a new operation command afterward.
4. When the Remote Setting screen appears:
   • Select the indoor unit.
   • Choose Heat Air Trigger Switch (Function 31).
   • Check the box next to the unit.
   • Click READ to view the current setting.
   • Enter the desired value (01 or 02) under Bulk Set.
   • Click the UP Arrow, then select WRITE to save.
5. The software will confirm if the write operation was successful.
6. After adjustment, the ROOM temperature in heating mode should more closely match the TH21 reading

See attached document for screenshots.