It only drives the fan so I guess it is a fan pulley.
Remove the 4 nuts that are against the pulley behind the fan with the belt still on the truck. Once these nuts are removed, the fan will separate from the pulley. Now you can remove the belt & water pump pulley.
The water pump is behind the pulley of the cooling fan---quite large and heavey
That is the water pump pulley.
On the front of the engine more or less behind the fan pulley. You'll see a domed section of water pipe...under there.
Put your new fan belt around the pulleys of your 1992 Chevy Blazer. Tighten the fan belt with the tensioner pulley.
if you do not have no experience in fixing car, do not do it
If it is a serpentine belt you replace the tensioner pulley
behind fan,bolted to front of engine block
Behind the fan blade and pulley.
There is no fan on the water pump on that vehicle, only a pulley that unbolts.
the water pump on the Chevy astros are right behind the fan. you need to remove the fan shroud, remove the belt, then the fan. The pulley comes right off and the part behind the pulley is the water pump. It is held on by four bolts two on each side. You will not be able to see them all, but they are reachable with a deep well socket, I believe a 9/16. I could be wrong about the size though. hope that helps :)
It's behind the pulley with the fan on