A report occurs during A/C operation when the low-pressure sensor installed at constant low-pressure parts detects a pressure of 0.05 MPa or less continuously for 2 minutes, or an instantaneous pressure of 0.02 MPa or less. (These values represent abnormal low pressure which may damage the compressor.)

However, the alarm does not actually occur the first 2 times that the above operation takes place. At these times, the outdoor unit is stopped and the conditions are monitored. The alarm occurs when the above operation occurs for the fifth time. The first 4 times before the alarm occurs are called “pre-trip.” After pre-trip occurs, if the low-pressure sensor detects a pressure of 0.15 MPa or more for 3 minutes of continuous operation, the pre-trip count is reset to 0.

If the low-pressure sensor detects a pressure of 0.16 MPa or less continuously for 30 minutes when the compressor is stopped, an alarm occurs immediately (no pre-trip). 

1. The absolute amount of gas in the system is too low (as a result of insufficient refrigerant charge or leak).
2. The refrigerant has accumulated in the circuit and has not returned to the compressor. Refrigerant has accumulated in a location of one-way flow and cannot escape. High-pressure level is low, resulting in poor flow of refrigerant in the circuit. (A lower high-pressure level results in a smaller difference between low pressure and high pressure, that may be insufficient to cause refrigerant flow.)
3. The refrigerant circuit has become closed, and refrigerant has not returned to the compressor. In some cases when moisture enters the refrigerant circuit, it can freeze at the low-pressure locations and the resulting ice can block the circuit.
   ☆ If the alarm occurs when there is sufficient refrigerant in the system ((1) and (3)), liquid refrigerant has definitely accumulated somewhere in the system. Liquid refrigerant generally accumulates in high-pressure locations. In this case the high pressure gradually increases (however it may not increase if the location where the liquid accumulates is sufficiently large). Depending on the refrigerant saturation temperature, it may also accumulate in low pressure locations. In this case the high pressure is unlikely to increase.

1. Check that the service valve is open.
2. Check that none of the valves (solenoid valves, mechanical valves) in the main refrigerant circuit is closed due to an operation failure.
3. Check that there is no possibility of foreign objects or water having entered the refrigerant circuit. (4) Check that valve leakage at a stopped sub unit has not resulted in accumulation of refrigerant at that sub unit. (5) Check that no refrigerant leakage has occurred.

1. If there was a valve operation failure, in general it is necessary to replace the valve.
2. If a foreign object or moisture has entered the circuit, install a strainer or dry core (depending on the degree of the problem).
3. If refrigerant has leaked into stopped sub units, it is likely that valve leakage has occurred. The valve must be replaced.