GENERAL Assist Technical Reference
VRF Indoor Functions
Auto restart, icing protection, oil recovery and outdoor-temperature protection
Technical reference covering automatic indoor-unit functions and suction-air-temperature protection logic.
These functions are automatic system-control operations. They may change fan operation, EEV position, operating mode or thermostat state when the relevant conditions are met.
1. Auto Restart
Following restoration of power, the air conditioner restarts using the previous operating settings.
2. Icing Protection Control
Icing protection prevents the indoor heat exchanger from icing during cooling and dry mode operation.
2.1 Starting conditions
Icing protection starts when either of the following conditions is satisfied:
| Condition | Requirement |
|---|
| 1 | Compressor has operated for more than 3 minutes, and heat-exchanger inlet temperature ≤ TA continuously for 4 minutes or more. |
| 2 | Compressor has operated for more than 3 minutes, and heat-exchanger outlet temperature ≤ TA continuously for 4 minutes or more. |
2.2 Operation during icing protection
| Indoor EEV | Closed |
| Indoor fan | Operates at the setting amount. |
2.3 Completion condition
Icing protection is completed when the heat-exchanger inlet and middle temperatures are ≥ TB after more than 5 minutes.
Drain-pump operation: The drain pump turns off 60 minutes after completion of the icing-protection operation.
3. Indoor-Unit Oil Recovery Operation
Oil recovery periodically returns residual refrigerant oil from the indoor unit and connecting pipework back to the outdoor unit. This prevents the compressor oil level from decreasing.
3.1 Indoor-unit indication
During oil recovery, the indoor-unit operation LED blinks in the following repeating pattern:
| LED state | Duration |
|---|
| ON | 6 seconds |
| OFF | 2 seconds |
| Pattern | Repeats as blinking indication |
3.2 Indoor-unit operation
| Indoor fan | Same operation as before oil-recovery operation. |
| Indoor EEV | Controlled by pulse. |
Normal operating characteristic: Refrigerant noise may be heard from the indoor unit during oil-recovery operation.
4. Outdoor-Temperature Protected Operation for Outdoor-Air Unit
The operating state is controlled according to the suction airflow temperature. Different thresholds apply depending on operating mode and whether operation-mode management is performed by an indoor unit with the outdoor-air unit acting as the master indoor unit.
4.1 Cool operation
A. Operation-mode management by indoor unit, with outdoor-air unit as master indoor unit
| Suction airflow temperature | Temperature rises | Temperature drops |
|---|
| High-temperature transition | At 20°C: Fan operation → Cooling operation | At 18°C: Cooling operation → Fan operation |
| Mid-temperature transition | At 10°C: Heating operation → Fan operation | At 5°C: Fan operation → Heating operation |
| Low-temperature transition | At -5°C: Forced thermostat OFF / fan OFF → Heating operation | At -7°C: Heating operation → Forced thermostat OFF / fan OFF |
B. Cases other than A
| Suction airflow temperature | Temperature rises | Temperature drops |
|---|
| Upper transition | At 20°C: Fan operation → Cooling operation | At 18°C: Cooling operation → Fan operation |
| Lower transition | At 10°C: Forced thermostat OFF / fan OFF → Fan operation | At 5°C: Fan operation → Forced thermostat OFF / fan OFF |
4.2 Heat operation
| Suction airflow temperature | Temperature rises | Temperature drops |
|---|
| Upper transition | At 21°C: Heating operation → Fan operation | At 19°C: Fan operation → Heating operation |
| Lower transition | At -5°C: Forced thermostat OFF / fan OFF → Heating operation | At -7°C: Heating operation → Forced thermostat OFF / fan OFF |
4.3 Fan operation
A. Operation-mode management by indoor unit, with outdoor-air unit as master indoor unit
| Suction airflow temperature | Temperature rises | Temperature drops |
|---|
| Upper transition | At 10°C: Heating operation → Fan operation | At 5°C: Fan operation → Heating operation |
| Lower transition | At -5°C: Forced thermostat OFF / fan OFF → Heating operation | At -7°C: Heating operation → Forced thermostat OFF / fan OFF |
B. Cases other than A
| Suction airflow temperature | Temperature rises | Temperature drops |
|---|
| Transition | At 10°C: Forced thermostat OFF / fan OFF → Fan operation | At 5°C: Fan operation → Forced thermostat OFF / fan OFF |
Service interpretation: The different temperature thresholds for rising and falling suction-air temperature provide hysteresis. This prevents rapid switching between operating states near a single temperature point.
Important: Forced thermostat OFF, fan stopping, mode changes and LED blinking described above can be normal control behaviour when the applicable protection or oil-recovery conditions are active.
