A receiver drier assembly for an automotive heat exchanger is provided with a single-piece cap. In embodiments described herein, a modulator has a tubular wall and one or more openings are formed therein. The cap is a single-piece cap and is configured to attach directly to the tubular wall via a snap fit. The cap may have a protrusion that is configured to snap into engagement with the opening in the modulator when properly assembled. The protrusion may be tapered such that as the cap is assembled to the modulator, the protrusion is forced radially inwardly via the tapered surface sliding along the tubular wall. Once the protrusion meets the opening, the protrusion is allowed to flex radially outward toward its natural unbiased position, snap fitting with the opening of the tubular wall.