My vents have stopped working. Air only comes out of the defrost. My truck has Warn manual lock out hubs. Apparently it came factory with ESOF hubs cause the old vacuum lines that went to the hubs are still there, just disconnected and it has the ESOF switch in the dash. I was thinking that the vacuum lines that ran to the old hubs being disconnected may be causing a vacuum leak but my vents were working fine until yesterday. I've searched and found some threads showing me which lines to check and I'll be doing that in a few minutes. How do I test the vacuum pump itself and the vacuum pump solenoid? What other functions in this truck are vacuum controlled? Sorry for all the questions, I'm still trying to get my mind wrapped around the PSD. I had my old IDI's figured out pretty well but this is a whole new ballgame!

Thanks,
Chuck

 

I believe you are on the right track, I to am leaning towards one of the lines leaking. The location of the vacuum pump is on the pasenger side, just behind the battery, check to make ure what ever they had plugging the lines is still there.

I do not have the answers to your other questions as of right now, sorry.

 

When you turn the key on and not start you truck, can you hear the pump running? It pulls a vacuum on a small canister and the lines run from that to your hubs and your vent control. I would plug the hubs off at the T near the pump.

 

Vacuum is only used for HVAC control and ESOF hubs.

If vac pump not running check fuse #28 underdash on 1999-2001. I don't have the fuse info for 2002-2003.

You can block both hub vac lines at the first 90° elbow connection on the hub vac line. Separate at elbow and block the line to the hubs and the one to the PVHS (Pulse Vacuum Hub Solenoid). With manual hubs you don't even need the PVHS.

 

I replaced the vacum pump on my truck (2000 350) a couple of summers ago, the pump was too weak to operate the blend doors properly and the A/C only blew air in the defrost position.