Defrost/Dash/Floor Vent Controls

[chardway]

I've just noticed that the moving the HVAC control knob on my 96 PS from "defrost" to "floor" to "vent" isn't changing anything. When I turn it to "off", the blower stops but in all other knob positions all the air seems to blow out all the openings (most from defrost vents).

I've only had the truck a couple of months and am new to diesels. Is there a separate vacuum pump for the HVAC controls? I recall that diesels don't produce manifold vacuum??? I checked the fuse list but none show "vacuum pump".

Any help would be appreciated. I don't have a shop manual yet.

[pipelayerjdh]

First of all, Welcome to the Forum!

Look under the dash, you will see a connector with several vaccume lines in it. Make sure it is plugged in. The most probable culprit is the solonoid that operates the airflow direction. Open the hood and look at the passenger side firewall. On top of the heater box there will be a potted meat can looking thing with a lever connected to one end and a vaccume line on the other. Trace that line to check for cracks. Have someone move the vent/def knob an see if it moves. There are no fuses for the vaccume pump, just one for the heater and fan controls. Check those and let us know if you need more help.

[chardway]

Thanks PIPELAYERJDH for the tips. I'll look for the items you noted once the rain stops!

By the way, where is the vacuum pump located?

[pipelayerjdh]

The pump is located between the AC compressor and PS pump.

[chardway]

Okay. Now I get it. The vacuum pump is belt driven (not electric like I initially thought). I found the problem with my vents; a vacuum hose at the "spherical" reservoir under the battery had come "off" (probably when I was digging around for the block heater electrical plug). Anyway, it's fixed now!

Thanks form the tips!