Do your HVAC vents change when you run through the selections? If they don't, and only come out through the windshield dash vent, that's another good indicator your vacuum is low.

 

X2^^^^^^^^

 

All of the vents operate properly. I acquired a chilton manual and a vacuum gauge. The chilton indicates a minimum of 18 inches hg and the vacuum is at 12 inches hg. I intend to replace the vacuum pump and convert to screw clamps on the hoses. I found no fault in the hoses but am considering replacing them because there was 2 inches less vacuum from the hose by the heater core. I question if the now available rubber hoses may be, like tires, less quality rubber that will deteriorate prematurely. Any thoughts on that?

 

Just for something to check, when my truck had a vacuum problem, I started chasing down vacuum lines and came up with the tiny plastic ones over by the heater core were rotting and falling apart. I made do with what I had, and just cut out the worst of it and put a rubber vacuum line on it. It's worked fine for a while now. My pump is still on it's way out, but I'm not too concerned about it since I'm going hydro-boost.

Long story short, those little plastic lines over by the heater core can rot, crack, and cause lots of problems that you wouldn't think of unless you saw them. You'll probably have to take them out of their protective sheath, too.

 

Thank you for the perspective, that would be an elusive diagnosis. With the hg gauge I did prove the vacuum pump to be failing. If there are further issues I will get into those plastic tubes.

 

Take the vacuum hose off the brake booster, start the truck and check for vacuum at that open hose. If you don't have vacuum there, then there's a problem between the pump and that point; possibly the distribution block that splits the vacuum out to the booster and the HVAC. If you DO have vacuum there, then you either have a bad booster, or that little check valve (the little plastic thingy that the hose goes onto, that's on the outside of the booster) has failed. Replacing that check valve would be the first cheap thing to try; if that doesn't change anything, it's probably new booster time.