A refrigeration system having a refrigerant compressor which has a refrigerant purity sampling circuit in parallel fluid flow communication therewith. The purity sampling circuit includes a refrigerant purity tube holder in which a refrigerant purity tube may be removably supported to thereby cause a flow of refrigerant therethrough during a purity sampling test due to the pressure differential across the compressor. The refrigerant purity sampling holder is adapted to receive an empty open ended test tube therein. The empty tube is left in the holder at all times, except when it is desired to perform a purity sampling test, in which case the empty open tube is removed and an active purity sampling tube is inserted therein. The system is further provided with the capability of purging the empty open ended tube and the refrigerant purity sampling circuit prior to the installation of an active tube.