Snare Drum = Harmonica Chugging
The chords created by drawing and blowing on the harmonica do not carry the same harmonic quality as chordal instruments such the guitar and piano, where they can choose the spacing (voicing), combination of notes (quality) and their inversions (which notes of the chord sound in which order). When playing "chordal" or what's often called "chugging" on the harmonica, it's not so much the "chords" we're playing that are the focus, but the rhythmic drive the pattern played creates. It's valuable to think of your chordal, rhythmic playing as being more similar to the rhythmic drive of the snare drum of the drum set. In the blues, the snare drum creates the consistent rhythm of the shuffle and train rhythm for example, or the accents (bombs) employed in that of the swing (where the ride cymbal carries the eighth note drive and snare is used for accenting). This focus on the rhythmic drive and/or accenting of off-beats of the snare will help you to take your chording/chugging on the harmonica to the next level.
For examples to play in this style visit the four lessons under "Solo Harmonica Study" as well as Joe Filisko's new series on the train.