A Google search for the word turns out just two results:
Yo estoy ya lista fresquita y bien arregladita lista para el pachongón
, where it is used in the sense pointed to by CarlosAlejo's comment: a degradation of pachangón as superlative of pachanga. Actually, the term pachangón is correctly used later in that text to talk about the same event.
A cual más gordito, mas tranquilo y mas "croquetoso" que ya con oir mi voz me hacen la rosca en la cuna ..... sin duda han salido al pachongón del padre
, where it seems to be used as superlative of pachón.
Anyways, it doesn't seem to be an extended word, nor one recognized by any dictionary.
If you need a translation, based on context you could use "big party" for the first scenario. The second scenario is trickier; you could maybe use "dull", "plump"...