My climate controls work only on setting 5 and only when blowing through the defroster. I think it may be a vacuum line issue, the only problem being I cannot find the vacuum lines under the hood. If anybody could tell me where to find a diagram of them online or suggest/know what the problem is (if my theory is incorrect), please let me know. The car is not supercharged and has a 3.8 engine.

is it ONLYwhen you have it on the defroster that the #5 speed works? because a common problem on these cars is the blower motor resistor, and that may be your problem

Yep. Settings 1-4 I get absolutely nothing. And when I switch it to another setting besides defrost, it is still blowing, but nothing is coming out.

If your blower works only on 5 then the resistors are bad. It is located under the dash on the pasenger side next to the blower motor. If your controls don't work, it is the control unit. I had the problem where my controls would just blow cool air. I thought it was a vacuum leak but it turned out it was internal and you need to replace the controls. Unit is about $200.00 but worth it to have Cold A/C in Summer and Hot air in winter.

The vacum line runs down by the battery to the vacuum reservoir in front of driver's side front wheel-- the line cracks and breaks due to battery acid venting onto it-- this is a very common problem on W-cars- I've fixed dozens of them this way by using a piece of rubber hose to splice it- this will get you the proper air delivery inside- the blower resistor needs replaced to get lower fans speeds

The vacum line runs down by the battery to the vacuum reservoir in front of driver's side front wheel-- the line cracks and breaks due to battery acid venting onto it-- this is a very common problem on W-cars- I've fixed dozens of them this way by using a piece of rubber hose to splice it- this will get you the proper air delivery inside- the blower resistor needs replaced to get lower fans speeds

My car would barly switch betewwn vents, yep found a check valve that supplies vacuume near the battery as you described badly acid dammaged.
THANKS !