Compressor Control
1. Compressor operating speed range
| Model | Cooling | Heating | Dry | ||
|---|---|---|---|---|---|
| Minimum | Maximum | Minimum | Maximum | ||
| AOTA72LALT | 28 rps | 90 rps | 28 rps | 90 rps | 42 rps |
| AOTA90LALT | 36 rps | 90 rps | 28 rps | 100 rps | 47 rps |
The AOTA90LALT has a higher minimum cooling speed than the AOTA72LALT and can operate at a higher maximum speed in heating. This reflects the different capacity and operating envelope of the larger model.
2. How compressor speed is controlled
During normal operation, the control board calculates the required compressor speed from several inputs. These commonly include:
- Difference between room temperature and set temperature
- Indoor and outdoor temperatures
- Heat-exchanger and compressor temperatures
- Refrigerant pressure and protection requirements
- The selected operating mode and current system load
| Operating condition | Typical compressor response | Purpose |
|---|---|---|
| High cooling load | Speed increases within the permitted range. | Increases refrigerant circulation and cooling capacity. |
| Low cooling load | Speed reduces towards the cooling minimum. | Avoids excessive cooling and improves temperature stability. |
| High heating load | Speed increases, subject to heating and protection limits. | Raises heating output and refrigerant mass flow. |
| Low heating load | Speed reduces towards the heating minimum. | Maintains comfort without unnecessary cycling. |
| Dry mode | The compressor uses the specified dry-mode speed. | Provides controlled moisture removal while limiting excessive room cooling. |
3. Normal start-up speed limitation
At start-up, the controller temporarily restricts the maximum compressor speed. The compressor can operate below the limit when demand is low, but it cannot exceed the active upper limit until the next stage is reached.
| Elapsed time after start | Maximum permitted speed |
|---|---|
| Start to 60 seconds | 33 rps |
| 60 to 180 seconds | 43 rps |
| 180 to 240 seconds | 55 rps |
| 240 to 300 seconds | 65 rps |
| After 300 seconds | Normal operating range and other active limits apply |
This staged increase allows refrigerant flow, pressure difference, oil circulation and heat-exchanger conditions to stabilise before the compressor is permitted to move into its full operating range. It also reduces sudden mechanical and electrical loading at start-up.
4. Cold-start control in heating mode
The service information applies the heating cold-start sequence when any one of the following conditions is present:
- The first compressor start after the power supply is turned on
- Compressor temperature is below 31°C
- The compressor has been stopped for eight hours or more
| Elapsed time after heating start | Maximum permitted speed |
|---|---|
| Start to 60 seconds | 33 rps |
| 60 to 120 seconds | 43 rps |
| 120 to 150 seconds | 55 rps |
| 150 to 210 seconds | 65 rps |
| After 210 seconds | Normal heating range and other active limits apply |
The cold-start sequence retains the same initial 33 rps limit for the first minute, then releases the upper-speed limits sooner than the normal start schedule. The practical effect is a controlled initial start followed by a quicker increase in available heating capacity once the first stabilisation period has passed.
5. What is normal during diagnosis
| Observed behaviour | Interpretation |
|---|---|
| Compressor starts slowly and increases in stages | Normal start-up upper-limit control. |
| Compressor remains below the graph limit | Normal if the calculated system demand is lower than the permitted maximum. |
| Heating output increases after several minutes | Expected as the speed restriction is progressively released and the refrigerant circuit stabilises. |
| AOTA90LALT reaches a higher speed in heating | Normal. Its heating operating range permits up to 100 rps, compared with 90 rps for the AOTA72LALT. |
| Speed remains limited after the start-up period | Check for active temperature, pressure, current, discharge-temperature, defrost or other protective control. |
6. Summary
- The inverter compressor changes speed to match system demand.
- Cooling and heating have model-specific minimum and maximum speeds.
- Dry mode uses a specified compressor speed of 42 rps on AOTA72LALT and 47 rps on AOTA90LALT.
- Start-up control limits the maximum available speed in timed stages.
- Normal start-up releases the 65 rps limit after 300 seconds.
- Heating cold start releases the 65 rps limit after 210 seconds.
- The compressor may operate below the limit whenever demand or another protection control requires it.