Air conditioner

An air conditioner having a refrigeration circuit including a first compressor of a low-pressure shell type which is always operated when only one of two units is operated;

• a second compressor of a low-pressure shell type which is stopped when only one of the two units is operated, the first compressor and the second compressor being connected in parallel;
• an equalizing pipe connecting together shells of the first and second compressors;
• a heat source unit-side heat exchanger;
• a throttling device;
• an indoor-side heat exchanger;
• and an accumulator, said air conditioner comprising:
• a bypass passage which branches off from a discharge pipe of the first compressor, a converging portion of discharge pipes of the first and second compressors, or a common discharge pipe located after convergence of the discharge pipes of the first and second compressors, and is connected to a suction pipe of the second compressor;
• an on-off valve disposed midway in the bypass passage;
• a liquid-level detecting circuit having one end communicating with a lower end inside the accumulator and another end connected to a discharge pipe of the accumulator;
• a heating means for heating the liquid-level detecting circuit and having a heating capacity falling within a range for heating the liquid-level detecting circuit so as to produce superheat vapor when wet vapor or saturated vapor flows through the liquid-level detecting circuit, or wet vapor or saturated vapor when the liquid refrigerant flows therethrough;
• a liquid-level temperature detecting means provided at an outlet of the liquid-level detecting circuit for detecting liquid-level;
• and
• a low-pressure detecting means disposed in a suction pipe of the first compressor, the suction pipe of the second compressor, or a common suction pipe of the first and second compressors,
• wherein when the first compressor is operated and the second compressor is stopped, the on-off valve is closed when a degree of superheat for liquid-level detection calculated from a temperature detected by the liquid-level-detecting temperature detecting means and a pressure detected by the low-pressure detecting means is greater than a liquid-level-detection superheat upper limit value set in advance, and the on-off valve is opened when the degree of superheat for liquid-level detection is less than a liquid-level-detection superheat lower limit value set in advance in such a manner as to be lower than the liquid-level-detection superheat upper limit value.