1992 Subaru Loyale 4wd and A/C switches (vacuum) doesn't work

1992 Subaru loyale, was sitting for about 2 weeks straight without use. . . I just changed the oil and spark plugs, and now the buttons for the 4wd and air conditioning/heater do not work. I heard that these are vacuum operated. Is this a quick fix? Will it lead to other problems? Brakes??

I would take a close look where you were working and make sure that any vacuum lines are still connected at both ends.   Since this could cause brake problems, I do recommend you consider this serious.  

The quick fix is finding the leak and fixing it.  You have an older car so it is not surprising that you are having a little problem or two on the system.  

While it is difficult to tell from here what the problem is a mechanic should be able to spot most such problems quickly.  However there is that occasional one that make life difficult. 

 You also may try listening when the car is idling and see if you can hear a hissing sound.  You might try using a length of garden hose like a stethoscope to find the source. 

Good Luck and be careful with those brakes until you have found and corrected the problem.