Vacuum tank question

92' Park Ave standard model
There is a black vacuum tank connected to the firewall right next to the fuse/ relay center. I noticed that the line going to it was disconnected while I was changing the oil (couldn't avoid a loud hiss!) I was just curious as to what this vacuum tank is for? When I stuck the line back on the engine idle dropped a little then came back up and ran perfect. Any ideas? Thanks in advance!

92' Park Ave standard model
There is a black vacuum tank connected to the firewall right next to the fuse/ relay center. I noticed that the line going to it was disconnected while I was changing the oil (couldn't avoid a loud hiss!) I was just curious as to what this vacuum tank is for? When I stuck the line back on the engine idle dropped a little then came back up and ran perfect. Any ideas? Thanks in advance!

That's the vacuum that operates the heater/AC vacuum motors inside the car to change the airflow in the heating unit! You should have been getting air only out the defrosters which is the failure mode with no vacuum. That way at least you can see safely if you're fogging up.

Alright, thanks for the info! I've been having some bad air flow problems, whether the tank is connected or not..I've cleaned the evap core, checked all of the vac hoses inside the dash and replaced the blower resistor with no results. Perhaps this vacuum tank is faulty?

my tank on my 95 PA was cracked at a seam. I replaced it and it almost completly fixed my problem (air changing to the windshield on acceleration). I must have another leak as well.