Yes, you can test many of the vacuum motors and the vacuum lines by using a hand operated vacuum pump (about $30 at many local parts stores). Make sure to buy one that has an integrated Vacuum Gauge, so you can watch and see if the system can hold vacuum once you apply it, -or if it leaks down. Some of the vacuum motors can be tested individually since they're on a part of the Climate Control "enclosure" on the outside, in somewhat accessable positions. Others might only be testable by removing the control head drawing vacuum on the cluster of hoses that plugs into the back of it. ...but you're going to need the service manual to figure out which vacuum lines do what.

There's one Climate Control manual on eBay right now, but it's for the 240 (click here) and the 240 is radically different from the ACC or MCC used in the 760/740. However, the seller is Skip Albright (also a board member here), and he might have the 700 series manual that you need. Contact him and see if it's available. Otherwise, contact me off-board and I'll see if I can walk you through the troubleshooting & diagnostic procedures (I have a copy of the manual myself at home, which I purchased 2 years ago from Skip).

If you do decide to start pulling apart Air Conditioning hoses (on either your 760 or the 740 parts car), take the car to a shop first and have the R12 recovered first. I don't what laws are in place where you live, but getting R12 credit points is like money in the bank (and much nicer on the environment). -and AC credit means cheap or free fills of R134a after you've converted the system.

God bless,
Fitz.