Now that I have my 1998 B1500 running good, I'm now working on another issue: I was checking the blower fan operation, it is getting warm like it should, but only comes out of the defroster ducts, no matter what position the selector **** is set to. I'm not hearing any noticeable vacuum leaks. Am I still looking at a vacuum issue? Previous owner was having this same problem

 

Yep. The vents are controlled by vacuum actuators. Defrost is the default setting if there is no vacuum. Likely there is a plastic line under the hood that broke..... they are plastic, and over time, harden, and become brittle. Look at 'em cross-eyed, and they disintegrate.

 

I checked the underhood ones,surprisingly they were in decent shape yet, but I can check them again.

 

I found a broken plastic vacuum line that ran down to the vacuum reservoir ball. I slipped a piece of slightly larger rubber hose over the break and taped it up. Started it ans let it run while I tested the various positions. Everything works as it should. Even idles better too. What size of rubber vacuum hose would be equivalent to replace all the underhood plastic lines? I may as well get rid of those brittle SOB's while I'm thinking of it

 

Same size you used to splice the broken line together.

 

Removed all the under hood plastic vacuum lines, just slightly bending them revealed many cracks along their lengths. Replaced all with brand new rubber lines

 

Do your vents work properly now?

 

Yes they do!!

 

Excellent.

 

thanks for the update