General Air Conditioning | Technical Support Reference
Ducted Fan Operation on Heat
Hidden function setting 33 = 04 to stop the indoor fan after the heating set point is reached
Overview: During heating operation, the indoor fan normally continues at a super-low or pulsed speed after the room reaches the set temperature. This is standard operation intended to maintain even room temperature and minimise sudden temperature swings.
Customer comfort concern: Some occupants may experience a cool draft once the heating demand has been satisfied. On compatible models, Function 33 = 04 can be used to stop the indoor fan completely at set point.
1. Function purpose
This setting changes the indoor fan behaviour in heating mode after the selected room temperature has been reached.
| Setting | Indoor fan behaviour at heating set point |
|---|---|
| Default factory setting | The indoor fan continues to operate in super-low or pulse mode. |
| Function 33 = 04 | The indoor fan stops completely once the heating set point is reached. |
Result: Stopping the fan prevents unheated air from being circulated through the ductwork after the system has satisfied the temperature demand, helping reduce cool-draft complaints.
2. How to enable the setting
Hidden function adjustment - wired wall controller
| 1 | Stop indoor unit operation. |
| 2 | Enter the Function Setting Mode on the wired wall controller. |
| 3 | Navigate to Function No. 33. |
| 4 | Change the setting value to 04. |
| 5 | Power down the indoor unit. |
| 6 | Leave the power off for a minimum of 5 minutes, then restore power and test operation. |
Important: The power cycle is required to ensure the revised function setting is stored and applied correctly.
Operating scope: This adjustment only changes indoor fan behaviour in heating mode. Cooling operation remains unchanged.
3. Model compatibility
Function 33 = 04 is only available on supported indoor units. Confirm the full indoor model and production date before applying the setting.
| Model series | Function 33 = 04 | Notes |
|---|---|---|
| LHTC | ✔ Available | Supported on units produced after January 2015. |
| LMLC | ✔ Available | Supported on units produced after January 2015. |
| LATU | ✖ Not available | Unsupported hardware. |
| LBTU | ✖ Not available | Unsupported hardware. |
| LHTDP | ✔ Available | Supported on all production runs. |
| ARTH - all H models | ✔ Available | Supported across the H-series ducted range. |
Compatibility check: Do not assume the setting is available based on controller type alone. Confirm the indoor unit model and, where relevant, its production date.
4. Summary
| 1 | The default heating behaviour is super-low or pulsed indoor fan operation after the set point is reached. |
| 2 | Setting Function 33 = 04 stops the indoor fan completely at set point to help reduce cool-draft complaints. |
| 3 | The indoor unit must be powered down for at least 5 minutes after changing the setting. |
| 4 | The function is supported on compatible LHTC, LMLC, LHTDP and ARTH H-series models, subject to the production requirements shown above. |
Technical reminder: After applying the setting, operate the system in heating mode and confirm that the fan stops after the room reaches set point and restarts correctly when heating demand returns.