mode switch question

[Delorean17@xxxx]

Hello,
When I purchased my car all of the vacuum lines were disconnected behind 
the mode switch. I hooked them up like they are supposed to be and none of 
the vent doors open except the floor vents. (I have the interior out of the 
car now so I can see them all) I also here a constant hissing sound from the 
switch. would this indicate a bad switch or is there something else I should 
try first? all hose connections are good.
also, when I drive with the A/C pump on I get a loud tick from the engine 
compartment at around 3500 RPMS but when i turn the AC off it goes away. 
any ideas on that?

Thank You
David