recirculation button : working or not

[bryan]

'87 n.a.

i'm trying to figure out if my recirc button is actually making air
recirculate.

i have the glove box off - on the side of the heater core, i seem to
have located a small enclosure that's connected by vacuum lines (?),
that makes a sharp "click" sound when i press the recirc button.
seems like a solenoid, but the vac lines... ? and it seems like
nothing happens between recirc/fresh settings (the button stays down
or up as expected).

does the "click" sound mean something in the part on the core has
failed? is this replaceable or does it mean the heater core needs to
come out, or i need to find a heater core to get a replacement?

thanks for any pointers

-bryan