The Difference Between Fixed Displacement and Variable Displacement in Car Air Conditioning
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The difference between fixed displacement and variable displacement compressors: 1. Fixed displacement compressor: Under different working conditions (temperature, speed, mode), the displacement remains unchanged, so the low-pressure changes are significant. Under high temperature and idle conditions, it can reach 3bar. Under low temperature and high-speed conditions, it is below 1.6bar (depending on temperature control) for defrost protection, with repeated fluctuations. Variable displacement compressor: When the suction pressure is above 1.6bar, the compressor always operates at maximum displacement. When the displacement is excessive, causing the low pressure to drop below 1.6bar, the displacement is reduced to maintain the low pressure around 1.6bar. Only in rare cases when the displacement is at its minimum, usually 10% of the maximum displacement, and the low pressure still drops, the compressor is cut off for defrost protection. 2. When the variable displacement compressor operates at full displacement, there is no difference in low pressure compared to the fixed displacement compressor. When the variable displacement compressor operates at small displacement, the compressor's low pressure is maintained at the set pressure, which is slightly higher than that of the fixed displacement compressor.
