General Assist Operating Guide
AST20AG / AOT20AN Wall Mounted Air Conditioner
Operation, timers, airflow, energy saving, cleaning and troubleshooting
Legacy wall-mounted system with wireless remote controller
This article summarises the operating instructions for the AST20AG indoor unit with AOT20AN outdoor unit. Some functions in the original operating manual are specifically marked as applying only to Heat & Cool (reverse-cycle) models; where relevant, this is identified below.
1. Quick operation
| Indoor unit | AST20AG |
| Outdoor unit | AOT20AN |
| Controller | Wireless remote control |
| Temperature setting range | AUTO: 18-30 °C; Heating: 16-30 °C; Cooling/Dry: 18-30 °C |
| Fan settings | AUTO, HIGH, MED, LOW |
| Air direction | Vertical and horizontal motorised adjustment, with independent swing functions |
To start the air conditioner:
- Press START/STOP. The indoor unit OPERATION indicator will illuminate.
- Press MASTER CONTROL to select the required mode. The manual shows AUTO, COOL, DRY, HEAT and FAN, with HEAT applying only to reverse-cycle models.
- Use SET TEMP to adjust the required temperature.
- Press FAN CONTROL to select AUTO, HIGH, MED or LOW.
Press START/STOP again to stop operation.
Remote control: Point the remote toward the indoor unit signal receiver. The manual specifies an operating range of approximately 7 metres. A beep confirms that the signal has been received.
Operating modes
| Mode | How it operates |
|---|---|
| AUTO | The system automatically selects an operating mode according to room temperature and the selected setting. On reverse-cycle models, AUTO can change between cooling and heating as required. |
| COOL | Used to cool the room. The fan may reduce to a very low speed during thermostat control. |
| DRY | Provides gentle cooling while dehumidifying. Fan speed cannot be manually selected in Dry mode. |
| HEAT | Reverse-cycle models only. Fan speed may remain very low temporarily after heating starts while the indoor heat exchanger warms. |
| FAN | Circulates room air without temperature control. The manual notes the temperature setting cannot be used while in Fan mode. |
2. Timer operation
Before using timer functions, ensure the remote control clock has been set correctly using the TIME ADJUST button and SET TIME buttons.
ON timer or OFF timer
- Press START/STOP if the unit is not already operating.
- Press TIMER until the required ON or OFF timer is selected.
- Use the SET TIME buttons to set the required time.
- The complete remote display returns after several seconds and the timer indicator remains displayed.
PROGRAM timer
The PROGRAM timer combines an ON and OFF timer into a single sequence. The manual allows OFF → ON or ON → OFF operation within a 24-hour period.
- Set the required OFF and ON timer times.
- Press TIMER until PROGRAM is selected.
- The air conditioner begins operating according to the programmed sequence.
SLEEP timer
Press SLEEP while the air conditioner is operating or stopped, then use SET TIME to select the operating duration.
- During heating, the thermostat setting is gradually reduced to avoid excessive heating while sleeping.
- During cooling/dry, the thermostat setting is gradually increased to avoid excessive cooling.
- When the selected time has elapsed, the air conditioner automatically stops.
3. Air direction and swing
The system provides motorised adjustment for both vertical and horizontal airflow direction.
| Function | Control |
|---|---|
| Vertical direction | Press AIR FLOW DIRECTION VERTICAL SET. Each press moves the flap through the available positions. |
| Horizontal direction | Press AIR FLOW DIRECTION HORIZONTAL SET to move the right/left louvers. |
| Vertical swing | Press AIR FLOW DIRECTION VERTICAL SWING. Press again to stop swing. |
| Horizontal swing | Press AIR FLOW DIRECTION HORIZONTAL SWING. Press again to stop swing. |
Do not move the airflow flaps by hand. The operating manual warns that manual movement may cause incorrect operation. Always adjust airflow using the remote controller.
4. Energy Save operation
The ENERGY SAVE function reduces energy consumption by automatically adjusting the thermostat setting.
- Start the air conditioner.
- Select COOL, DRY or HEAT mode as applicable.
- Press ENERGY SAVE. The ENERGY SAVE function operates while the selected mode is running.
- Press ENERGY SAVE again to cancel.
- Heating: the manual states the thermostat setting decreases by 1 °C as soon as Energy Save is selected, then decreases further over time to a total reduction of 4 °C.
- Cooling/Dry: the thermostat setting increases by 1 °C immediately and then increases further over time to a total increase of 2 °C.
Manual Auto operation
If the remote control is unavailable, the air conditioner can be operated using the MANUAL AUTO button on the indoor unit. The manual states that manual operation runs using AUTO mode settings.
5. Cleaning and care
Before cleaning: Turn the unit off and disconnect the power supply. Do not touch the heat exchanger fins while removing or replacing the air filters.
Cleaning the intake grille
- Open the intake grille and remove it as shown in the operating manual.
- Clean using water. Dust can first be removed with a vacuum cleaner, then the grille can be wiped with warm water and dried with a clean soft cloth.
- Refit the intake grille securely.
Cleaning the air filter
- Open the intake grille and remove the air filter.
- Remove dust with a vacuum cleaner or wash the filter.
- If washed, allow the filter to dry thoroughly in a shaded location.
- Refit the filter and close the intake grille.
The manual recommends cleaning the air filters approximately every two weeks during normal use.
6. Troubleshooting
Normal operating characteristics
| Symptom | Explanation from the operating manual |
|---|---|
| Does not operate immediately | After stopping and immediately restarting, the compressor may remain off for about three minutes to protect the fuse/circuit. A similar delay can occur after power is restored. |
| Noise is heard | Refrigerant flow can produce water-flow sounds. Expansion and contraction of the front cover may also cause occasional squeaking. |
| Smell | Room odours absorbed into the indoor unit can be emitted during operation. |
| Mist or steam | A fine mist can occur during cooling/dry due to sudden cooling of room air. Steam may occur during heating defrost operation on applicable reverse-cycle models. |
| Airflow is weak or stops | During heating, the fan may run slowly while the indoor unit warms. During automatic defrost, indoor operation may stop temporarily. In Dry mode, fan speed can be very low. |
| Water from outdoor unit | On reverse-cycle models, water may be produced during automatic defrost in heating operation. |
Checks before requesting service
- Confirm the power plug is connected and the circuit breaker has not tripped.
- Check whether there has been a power failure.
- Confirm a timer is not currently operating.
- Clean the air filter if it is dirty.
- Ensure the indoor air inlet and outlet are not blocked.
- Check that the selected temperature is appropriate.
- Ensure doors and windows are closed where practical.
- Check the remote-control batteries and confirm they are installed correctly.
Request service if: the problem remains after the checks above, there is a burning smell, or the TIMER indicator lamp flashes. Stop operation, disconnect the power supply and arrange authorised service.
7. Operating tips
- On applicable reverse-cycle models, heating performance reduces as outdoor temperature falls because the system operates as a heat pump.
- Automatic defrost may operate during heating when frost forms on the outdoor unit. During defrost, heating stops temporarily and the indoor OPERATION indicator flashes.
- After a power interruption, the unit can restart automatically once power is restored if it had been operating before the outage.
- For cooling and dry operation, the manual lists an outdoor operating range of approximately 21 to 46 °C and an indoor temperature range of approximately 18 to 32 °C.
- If indoor humidity is very high during cooling/dry operation, condensation may form on the indoor unit if operation continues for long periods.
Reference: Fujitsu Operating Manual, Room Air Conditioner - Wall Mounted Type, indoor unit AST20AG / outdoor unit AOT20AN, P/N 9366276012.