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Ｒ５０２曾广泛使用于商用低温制冷系统中，但因其中含有ＣＦＣ成分，它的使用受到限制。Ｒ４０４Ａ（由ＨＦＣ１２／ＨＦＣ１４３ａ／ＨＦＣ１３４ａ组成）是一种对大气臭氧层无破坏的，可长期替代Ｒ５０２的混合制冷剂。作者首先用ＣＳＤ状态方程对这两种工质的热力学与制冷循环特性进行了理论上的计算，然后，在一台可使用Ｒ４０４Ａ的风冷压缩冷凝机组上进行了一系列的试验。采用第二制冷剂量热器法来测量机组的制冷量。系统中加装了一个水过冷器来控制节流前液体温度。试验中，控制蒸发温度在－４０～－１０℃之间变化，环境温度为３２℃和４０℃。为了测定过冷的影响，在一定的环境温度和蒸发温度下进行了各种过冷温度的试验。在同一台机组上，相同工况下进行了Ｒ４０４Ａ和Ｒ５０２的对比试验。计算和试验结果表明，Ｒ４０４Ａ具有与Ｒ５０２相近的制冷性能，特别是在蒸发温度高和冷凝温度低的情况下。在低温范围，Ｒ４０４Ａ的性能比Ｒ５０２略有下降。在所测的温度范围内，Ｒ４０４Ａ的排气温度都比Ｒ５０２低，这有利于压缩机工作的可靠性。
R502 has been widely used in commercial cryogenic refrigeration systems, but its use is limited by its inclusion of CFC components. R404A (composed of HFC12 / HFC143a / HFC134a) is a long-term alternative to R502 mixed refrigerant that is non-destructive to the atmospheric ozone layer. The authors first calculated the thermodynamic and refrigeration cycle characteristics of these two refrigerants using the CSD equation of state. Then, a series of experiments were carried out on an air-cooled condensing condensing unit using R404A. The second refrigerant calorimeter method is used to measure the cooling capacity of the unit. A water subcooler is installed in the system to control the liquid temperature before throttling. In the experiment, the control evaporation temperature varied from -40 ℃ to -10 ℃, the ambient temperature was 32 ℃ and 40 ℃. In order to determine the effect of subcooling, various subcooling temperature tests were carried out at a certain ambient temperature and evaporation temperature. In the same unit, under the same conditions R404A and R502 comparative test. The calculation and experimental results show that the R404A has similar cooling performance to R502, especially at high evaporation temperatures and low condensation temperatures. In the low temperature range, R404A slightly lower than the R502 performance. In the measured temperature range, R404A exhaust temperature lower than R502, which is conducive to the reliability of the compressor.