Ah that's a huge help. I had no clue he only appeared at certain times, now i know when and where to look for him. Thanks guys.

He comes once a week from Friday morning to Sunday morning (U.S.). He sells a weapon, various armor, exotic shards, exotic engram, weapon telemetry, sparrow upgrades, and ammo synth.

Xur is a vendor who shows up on the friday reset and goes away on the sunday reset. He has a total of around ten places in the tower he can show up for that weekend, but is in one place for the entire weekend. He is somewhat of a blackmarket seller. He sells exotic weapons and gear for strange coins, and sometimes has exotic engrams, heavy ammo synth, weapon telemetries and sparrow upgrades. There are some exotic bounties where you need to buy an item from xur, this item will only show up when you have to buy it. Xur also has exotic upgrades, only use this for exotics gained before the dark below DLC, it is meant to bring them to 36 light or 331 damage. It will reset the progress on 331/36 exotics.