Capillary tubes are generally used as throttling devices in packaged units of household compressor refrigerators, air conditioners and heat pumps. Successful experience in their application into the units of the cooling capacity of more than 20 kW have also been achieved. In spite of wide use, the following problems are not yet fully explained: mathematical modelling of the throttling process at two-phase metastable flow, conditions of a critical flow, effect of heat exchange on the throttling process, capacity control end effect of the use of capillary tubes.