GENERAL Assist Technical Reference
J Series Compressor Control
Capacity control, operating frequency and compressor speed hold logic
Technical reference for J Series compressor operation
The J Series varies compressor rotation speed according to system demand. Capacity is calculated differently in cooling and heating, while compressor frequency is also corrected by operating conditions and protective controls.
1. Capacity Control
Cooling
The compressor rotation speed is determined from the sum of the required refrigerant amount from the connected indoor units.
Heating
- Compressor rotation speed is determined by detecting the indoor heat exchanger mid temperature of connected indoor units operating in heating mode.
- The control adjusts compressor speed so the detected temperature reaches the target temperature.
- The compressor is controlled by PI control.
- During heat exchanger temperature detection, one of the largest signals from the indoor units operating in heating is used to determine compressor rotation speed.
- At compressor start-up, rotation speed is determined from the sum of the required refrigerant amount.
2. Frequency Control
| Operating Condition | Compressor Frequency |
|---|---|
| Stop mode | 0 Hz |
| Operating mode | 20 Hz to approximately 100 Hz |
| Minimum running frequency | 20 Hz |
Frequency correction
The compressor control frequency is corrected according to the following conditions:
- Outdoor temperature
- Pipe length setting
- Capacity shift setting
- Protective operation
Protective control has priority: When a protection function is active, protective frequency correction takes the highest priority.
Operating current limit
Operating current is limited in accordance with the applicable DIP switch setting.
3. Compressor Rotation Speed Hold
When the compressor starts after being stopped, compressor speed is held within defined periods so it does not immediately increase to the desired speed. This helps avoid a sudden drop in compressor oil surface level.
If the target speed falls below the held speed while the hold is active, the speed hold is released.
| Hold Stage | Held Frequency | Duration / Timing |
|---|---|---|
| Hold 1 | 50 Hz | 230 seconds |
| Hold 2 | 70 Hz | 550 seconds from compressor start-up |
Simplified compressor speed hold sequence
| Frequency | Start-up → 50 Hz Hold 1 → increase → 70 Hz Hold 2 → increase toward target speed |
| Timing | 230 sec at Hold 1 | 550 sec from start-up to end of Hold 2 |
4. Technical Summary
| Cooling capacity demand | Based on the total required refrigerant amount from connected indoor units. |
| Heating capacity demand | Uses indoor heat exchanger mid temperature and PI control. |
| Operating frequency range | Approximately 20 to 100 Hz, with 20 Hz minimum running frequency. |
| Protection | Protective correction overrides normal frequency correction when active. |
| Start-up hold | 50 Hz for 230 seconds, followed by a 70 Hz hold with the second hold ending 550 seconds after start-up. |
Source: J Series technical information — Compressor Operation, Capacity Control and Frequency Control.