Vacuum issues

[Bgirls]

While on a trip to Ohio this past week we lost the ability to direct the AC through the dash vents. It has defaulted to blowing through the defrost vents. Also have a small vacuum pump on the right fender well that seems louder than ever before. Where are the typical trouble spots in the vacuum system and does the vacuum system have anything to do with the shifting to 4 low?

 

[Double-S-Diesel]

good possibility a vaccum line to the hubs is bad.
this will allow a vac leak and the pump to run nonstop.
or the vac pump may be bad.
default at loss of vaccum is the defrost pos only.

 

[Bgirls]

besides the heat/ ac system what else is operated by vacuum?

i was just doing a search in older posts and wanted to clarify that the vacuum pump i am talking about running constantly is not on the front of the engine and belt driven, it is mounted on the passengers fender and electric driven.

 

[Bgirls]

i have done some diagnosis, i bypassed all but the climate system and the pump now shuts off and the climate system fuctions properly. near this vacuum pump there is another electric/vacuum/switch ? that maybe has to do with the 4 wheel drive system but makes no difference if the 4x4 is activated or not the system operates the same. does anybody have an idea what i am talking about?

 

[NCheek]

On trucks with the Electronic Shift on the Fly 4x4, the vacuum controls the climate control in the cab, and the engagement of the automatic hubs. Seems like something about the vacuum system that runs the hubs is always screwing up on my dads truck, because I have torn into that axle several times...

 

[Double-S-Diesel]

that other switch is for the hubs
good chance the switch is bad , especially if the hubs ingage

 

[Bgirls]

i have tested and determined it to be the PVH solinoid. the Pulse Vacuum Hublock. fancy words for the vacuum hub controller. all other tests good except an ohms reading should be 45-55 and mine is at 90.
will know for sure when the new one arrives.

 

[Bgirls]

I replaced the PVH switch and my problem is solved. The hardest part was getting the part delivered. At one point it was a 1/2 mile from my home and then went back to Nevada. I gave them a billing address which is a P.O box, and a physical address which is the house. They shipped by u.s. mail to the physical address which does not have postal delivery.