Overview
By default, when a ducted system is operating in heating mode and the set temperature is reached, the indoor fan continues to run at a super low or pulsed speed.
This is standard operation designed to maintain even temperature distribution and prevent sudden swings in room temperature.
However, some occupants may notice a cool draft when the fan continues to operate after the space has already reached the heating set point.
To improve comfort, a hidden control function allows the indoor fan to stop completely when the heating set point is reached.
1. Function Purpose
This feature enables the technician to modify fan behavior in heating mode once the set temperature has been achieved.
| Setting | Behavior |
|---|---|
| Default (Factory Setting) | Indoor fan operates in Super Low / Pulse Mode when the set point is reached. |
| Modified (Function 33 = 04) | Indoor fan stops completely once the heating set point is reached. |
This prevents cool air from being circulated after the system has satisfied the temperature demand.
2. How to Enable the Setting
Hidden Function Adjustment – Wired Wall Controller
Stop indoor unit operation.
Enter the Function Setting Mode on the wall controller.
Navigate to Function No. 33.
Change the setting value to 04.
Power down the indoor unit.
Leave power off for a minimum of 5 minutes before restarting to ensure the new setting is stored.
Note:
This adjustment only affects heating mode fan behavior.
Cooling operation remains unchanged.
3. Model Compatibility
This hidden fan stop function is available on certain models produced after January 2015, as listed below:
| Model Series | Function 33 = 04 Availability | Notes |
|---|---|---|
| LHTC | ✅ Available (post-Jan 2015) | Supported |
| LMLC | ✅ Available (post-Jan 2015) | Supported |
| LATU | ❌ Not Available | Unsupported hardware |
| LBTU | ❌ Not Available | Unsupported hardware |
| LHTDP | ✅ Available | Supported on all production runs |
| ARTH (All “H” Models) | ✅ Available | Supported across all H-series ducted models |
4. Summary
Default fan behavior on heating is low or pulsed fan speed at set point.
Setting Function 33 = 04 stops the fan completely to reduce cool draft complaints.
Power must be cycled after applying this change.
Available on LHTC, LMLC, LHTDP, and ARTH (“H” series) models produced after January 2015.