York purge?

i know you can get the emergancy pressure release for you air systems, but do yorks have one built in? cause last night we fired up my truck for the first time since the body drop... i hooked the clutch up on the york and it started pumpin.. then a lil while later it started blasting bursts of air outta the hole in the back, like a purge would... just wondering what caused that? cause i haven't turned it back on since then just in case....