What part is this?

Hello everyone, I'm curious what that grapefruit-size plastic piece mounted to the hood that a vacuum line is attached to on my '94 s-10. I'm thinking I read somewhere that this might be related to my problems with my air not coming out of my vent, but out of the defrost and floor. Any details on what this is would be great!

Always learning something new on here.

That is your vaccume resivoiur... Make sure that the hose is attached and there aren't any cracks in it.

My truck was doing that last year. Mine is a '95 though so I'm not sure if it is the same setup. But my heater control knobs were all vacuum controled and the seals inside the control were all dirty and dried out. I ended up taking the control apart and cleaning it all and putting a little 3 in 1 oil on it and haven't had any problems since. 3 in 1 oil might not have been the best for it but that's all I had at the time. Hope it helps.

i'm not sure about yours but i had a 95 grand am that had a very similiar problem, i talked to a mechanic at the dealer and he said that there would be a vacumn line (gray) between the headlight and battery on the drivers side that would be shafed and leaking. he was right once i spliced it, it was fixed i don't know it the lines on a s10 are in the same place but someone at the dealer will probly know good luck

i'm not sure about yours but i had a 95 grand am that had a very similiar problem, i talked to a mechanic at the dealer and he said that there would be a vacumn line (gray) between the headlight and battery on the drivers side that would be shafed and leaking. he was right once i spliced it, it was fixed i don't know if the lines on a s10 are in the same place but someone at the dealer will probly know good luck

It could be a problem with the vaccum switches too. I had the same problem with my truck when I bought it and found out one of the vaccum switches was broken off. Here's a picture I took when I found the broken mount.
(looking up with back of head on brake pedal)
http://i10.photobucket.com/albums/a101/joblo33/1e7060f0.jpg
The vaccum switch on the left controls the Heater/Vent-Defrost switch, and the one that goes where that broken mount is controls Vent/Defrost. You probably have a problem, if not the same problem, with the switch that broke off on mine.
Good Luck,
Eric