General Assist Technical Reference
Indoor Unit Control
Fan speed, AUTO operation, Dry mode and master control logic
Technical operating reference for AIRSTAGE indoor unit control behaviour.
This article explains how the indoor unit controls fan speed in manual and AUTO settings, how fan speed changes in Cooling and Heating, the operating sequence in Dry mode, and the basic master control logic used for the indoor fan, drain pump and electronic expansion valve.
1. Fan speed setting
Press the FAN CONTROL button to select the required indoor fan speed.
| Setting | Operation |
|---|---|
| AUTO | The indoor unit automatically selects fan speed according to operating mode and the difference between room temperature and set temperature. |
| HIGH | Fixed high fan speed. |
| MED | Fixed medium fan speed. |
| LOW | Fixed low fan speed. |
2. AUTO fan position
Temperature reference: Tr = corrected room temperature and Ts = corrected set temperature.
Cooling operation
In Cooling, fan speed is automatically selected from the difference between room temperature and set temperature. Different thresholds are used depending on whether the room temperature is decreasing or increasing.
| Fan speed | When room temperature decreases | When room temperature increases |
|---|---|---|
| High | Tr - Ts ≥ 2°C | Tr - Ts ≥ 3°C |
| Medium | 1°C ≤ Tr - Ts < 2°C | 2°C ≤ Tr - Ts < 3°C |
| Low | Tr - Ts < 1°C | Tr - Ts < 2°C |
The fan speed zone is re-evaluated when the set temperature is changed, when the operating mode is changed to COOL, or when fan control is changed to AUTO.
Heating operation
In Heating, fan speed is also decided by the difference between room temperature and set temperature.
| Fan speed | When room temperature decreases | When room temperature increases |
|---|---|---|
| Low | Tr - Ts > -2°C | Tr - Ts > -1°C |
| Medium | -2°C ≥ Tr - Ts > -3°C | -1°C ≥ Tr - Ts > -2°C |
| High | Tr - Ts ≤ -3°C | Tr - Ts ≤ -2°C |
3. Dry operation
Key behaviour: In Dry mode, the indoor fan always rotates at Low speed.
| 1 | The indoor fan normally starts approximately 5 seconds after the electronic expansion valve opens. |
| 2 | When the indoor unit has just started or the operating mode has just changed from another mode to DRY and refrigerant circulation has not stopped, the fan can rotate immediately without the 5-second delay. |
| 3 | The indoor fan stops approximately 30 seconds after refrigerant circulation stops. |
| 4 | The fan stops immediately if the indoor unit is stopped by the stop button or by an OFF timer setting. |
| 5 | If refrigerant circulation stops because room temperature remains low for more than 3 minutes, the fan rotates for approximately 2 minutes at intervals of 3 minutes. |
| 6 | When Dry mode begins after another operating mode and refrigerant circulation has stopped, the fan rotates for approximately 1 minute before following the normal Dry mode sequence. |
4. Master control - operation mode control
Stop mode
| Indoor fan motor | OFF |
| Electronic expansion valve | Stop pulse |
| Drain pump | Turns ON/OFF according to the drain pump control function. |
Cool, Dry and Heat mode
| Component | Cool | Dry | Heat |
|---|---|---|---|
| Indoor fan motor | Operates according to the AIR FLOW-MODE setting. | See Dry mode fan control sequence above. | Operates according to the AIR FLOW-MODE setting and cold-air prevention operation. |
| Drain pump | Turns ON/OFF according to the drain pump control function. | ||
| Electronic expansion valve | Pulse controlled by temperature difference calculation and frost prevention function. | Pulse controlled by temperature difference calculation and frost prevention function. | Pulse controlled by the temperature difference. |
5. Priority mode
Priority mode is used to restrict heating, cooling or dry operation commands from connected indoor units. The source material identifies three priority modes.
| Priority mode | Restricted operation mode |
|---|---|
| Neutral | No restrictions |
| Cooling priority | Heating |
| Heating priority | Cooling and Dry |
Technical note: This article reproduces the control logic shown in the legacy Indoor Control technical reference. Always confirm the applicable service documentation for the specific indoor unit model before using these values for diagnosis.
General Assist – AIRSTAGE Technical Information