Abstract: When the content of indoor air conditioning unit is too small or too large, it will cause adverse effects on the heat exchanger. In order to find a suitable range of internal and external machine volume to maximize the common and replacement design, uses the experimental method to test the matching of internal machine with different volume of 24K model, and carries on the actual verification to many brands of internal machine. The results show that when the content product ratio of frequency conversion products is between 50% and 91%, the output capacity of the products is the same, and the products can be interchanged, so as to meet the performance requirements of the North American products.

Key words: Volume, Ratio, Air handler unit, Replacement