AIRSTAGE Technical Reference
Enabling FAN Mode on Compatible VRF Indoor Units
Function setting 99 for independent indoor fan operation
Applicable only to indoor units with the required updated control-board software
FAN Mode can be enabled on certain VRF indoor units following a software update that introduced inverse logic control for external inputs. When supported and enabled, the indoor fan can operate without selecting heating or cooling.
Compatibility must be confirmed first: Check the applicable serial-number or software-version list before changing Function 99. Unsupported units may not display FAN Mode even after the setting is changed.
1. Background
Historically, FAN Mode was restricted on VRF indoor units because residual refrigerant may continue to pass through an indoor coil while other units on the same system are operating.
As a result, the air delivered during fan-only operation may feel slightly warmer or cooler than room temperature, even though the indoor unit is not actively calling for heating or cooling.
Customer expectation: FAN Mode provides air circulation only, but it does not guarantee completely neutral discharge-air temperature under all system conditions.
2. Applicability
This function is available only on indoor units fitted with the updated control-board software that supports inverse logic control.
| Check | Requirement |
|---|---|
| Indoor unit compatibility | Model and serial number must appear on the applicable compatibility list. |
| Control-board software | The installed software version must support Function 99 FAN Mode operation. |
| Remote-controller display | FAN Mode will become selectable only when the indoor unit supports the function and Function 99 is enabled. |
3. Procedure - Enable FAN Mode
- Access the indoor unit's Function Setting Mode using the applicable remote-controller procedure.
- Locate Function 99.
- Change the setting from 00 - Disabled to 01 - Enabled.
- Exit Function Setting Mode and confirm that FAN Mode is now available on the remote controller.
| Function | Setting value | Operation |
|---|---|---|
| 99 | 00 | FAN Mode disabled - default setting |
| 99 | 01 | FAN Mode enabled on compatible units |
4. Important operating notes
- FAN Mode is disabled by default to reduce unwanted temperature effects caused by residual refrigerant circulation.
- When enabled, the function provides air circulation without intentionally commanding heating or cooling.
- A minor change in discharge-air temperature may still be noticeable, depending on the operating condition of other indoor units.
- Normal heating and cooling operation is not affected by enabling this function.
- Only enable FAN Mode where the customer specifically requires fan-only operation and understands the possible temperature variation.
5. Technical support guidance
| Situation | Recommended action |
|---|---|
| Customer requests fan-only operation | Confirm compatibility, explain the potential for slight heating or cooling, then enable Function 99 where appropriate. |
| FAN Mode does not appear after changing Function 99 | Reconfirm the indoor unit's serial number and software compatibility. Unsupported software will not provide the selectable mode. |
| Air feels slightly warm or cool in FAN Mode | Advise that residual refrigerant flow may affect coil temperature while other units on the system are operating. |
| Normal heating or cooling concern after enabling | Diagnose the operating concern separately. Function 99 does not change normal heating or cooling control. |
Service summary: Verify compatibility first, set Function 99 to 01, confirm FAN Mode appears, and explain that residual refrigerant flow can create a small discharge-air temperature change.