I need serious help; tried a search, but could not find a related post. Last night, the ignition switch failed to shut off the engine on my '80 300SD. Used the shut off lever under the hood, and knew to get up early this morning and check the vacuum lines. Nothing obvious loose or broken, so I figure I have a stoppage somewhere. On my way into town, I noticed, too, that my A/C center vents weren't issuing any air. I was further convinced of a vacuum problem. About a half-hour later, I started back home, and the A/C would not run at all. The compressor isn't kicking in, and no air comes from any vents. I know the old auto temp system has vacuum lines going into the back of the unit, so I now figure there is a problem with that system, but vacuum related just like the shut off. My door, trunk, and fuel door locks still work. Can someone point me in a direction that will get me to a successful fix for this problem? The heat index here in Northeastern Arkansas is 99° today, and I hate to be hot.

Thanks in advance for any and all help