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Topic: Dash Air Stuck on Defrost/Vacuum Pump Replacement (Read 3213 times) previous topic - next topic

Dash Air Stuck on Defrost/Vacuum Pump Replacement

It took me a fair bit of time to piece the how-to information together from different posts (and the "why") so I thought I'd do an updated post with part numbers and detailed pictures. This is really intended for the "next guy", so please chime in if missed something.

In the 01 U320, the dash air is controlled by a vacuum. If the system isn't able to create a vacuum, it's unable to change which dash vent the air goes to. When this happens, it defaults to the defroster vents right next to the windshield. There is a vacuum generator (powered by an airline) behind the front entry step that goes out. When this happens, the solve is to replace it with an electric vacuum pump. Here's what you will need:

    • A new vacuum pump. $70 on Amazon. Part #: 53032373AB Note that you can also buy this from MOT, for $200. It's slightly different and won't require the wiring harness below.
    • 3 self tapping screws to secure the new pump
    [/list]

    Steps:
      • Test for power going to the vacuum generator first by disconnecting the plug and hooking up with a voltage meter. With the ignition on, you should get 12v at the plug. If not, hunt that down first as the rest of this may not be needed.
      • Assuming you have 12v at the plug, disconnect the plug and snip the two wires coming from the vacuum generator, and set the plug aside. You will reuse it later.
      • Block your suspension with safety blocks
      • Remove the air line going into the vacuum generator. It will blow air. I don't think it's part of the same run that your air bags are tied to, but you'll need to crawl under the rig later in the process so you might as well block the suspension before doing this.
      • Remove the vacuum generator
      • Take the plug that you saved and connect those two wires to the green and black wires on the wiring harness you bought. It does not matter which black wire goes to green/black on the harness. The other two wires on the wiring harness are not needed and can be removed/capped off. Ultimately, what you're trying to do is deliver power to the 2 corresponding pins on the new vacuum pump
      • The new vacuum pump will come with a little white rubber nipple over the intake port to protect it. Because the inside diameter of the line coming from the drum is larger than the OD of the fitting on the pump, we'll use this to act as an adapter. Snip the end off the rubber nipple and put it on the fitting. Then wrap in electrical tape to make it a little thicker. Do a snugness test to make sure you have a tight fit on the vacuum line going into the vacuum
      • With the rig blocked, follow the airline from behind the entry step, to the backside of the "box" you're working in. Find where it comes to a "T". Remove the line from that T and insert your 1/4 plug with Teflon tape
      • Mount your new vacuum pump where the old one used to be. It's a little tricky to secure due to the limited space. I used a flexible drill bit extension and self tapping screws. Make sure both the vacuum line coming from the drum and the 12v wires can reach the location of the pump.
      • Connect the vacuum line and plug the wiring harness in on each end.
      • Cross fingers and toes
      • Turn ignition on and test the dash air by fiddling with the knobs
      [/list]
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      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #1
      I suggest you also replace the vacuum bottle - it looks like a tin can and is starting to rust out.  You can just see it to the left in the last picture.  They make them out of plastic now and they spherical and about the size of a small cantaloupe.

      Rich

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #2
      I suggest you also replace the vacuum bottle - it looks like a tin can and is starting to rust out.  You can just see it to the left in the last picture.  They make them out of plastic now and they spherical and about the size of a small cantaloupe.

      Rich
      I know that can also be a source of leaks so it's been on my radar. Can you explain how it works/what role it plays in the vacuum system?

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #3
      Can you explain how it works/what role it plays in the vacuum system?
      Elliott,

      Think of it as a surge tank/storage tank.  It keeps the vacuum pump from short cycling every time a vacuum is called for.

      Mike

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #4
      This is how my set up looked. Keeps your pump from running as much



      Keith

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #5
      Keith do you have the part number still for the replacement tank? Did you reuse the old
      Line between pump and tank?

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #6
      Keith do you have the part number still for the replacement tank? Did you reuse the old
      Line between pump and tank?
      All that you see is new hooked to the original hose going to the dash

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #7
      I got my tank at NAPA online with local pickup.  It saves a few bucks over going direct to the store.

      Kieth - the first picture you posted is actually one of my setup.  I recognize the tools and handwoven towel from my wife.  I found that poly cutting board on the beach in Alaska and knew it would be useful eventually.

      Rich

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #8
      Where is the vacuum generator or the 270s? Our 99 320 was set up just like Elliott's but I don't see it on this 270. Thanks.
      jor

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #9
      Mine was behind the fold down entry step.

      Rich

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #10
      That's the way our 320 was but here's what it looks like on this one.
      jor

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #11
      I got my tank at NAPA online with local pickup.  It saves a few bucks over going direct to the store.

      Kieth - the first picture you posted is actually one of my setup.  I recognize the tools and handwoven towel from my wife.  I found that poly cutting board on the beach in Alaska and knew it would be useful eventually.

      Rich
      Whoops, I built one identical to it but my board was a little different, built it was off your design..  couldn't remember who posted up on how to build it. It was on the 2000 I sold last year..  it worked great by the way!


      Keith


      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #13
      Quote
      Joe where is the pump?
      Was this directed at me (jor) or Joe from Keith & Joe? If me, that's the question. Where's the pump?
      jor

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #14
      What is on the other side of that panel in your photo (Reply #10)?

      Those two brass "T" fittings must connect to something on the other side of the panel.

      That would be a possible location for the pump?

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #15
      Quote
      What is on the other side of that panel in your photo
      Just the valves for the step and step cover. Here's a photo. I never thought about the location of the vacuum stuff on this one but now it's driving me crazy.
      jor

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #16
      Mine is in front behind the lights on the passenger side I believe.

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #17
      JOR - Those two valves control the step and the vacuum generator.  Follow the air lines to the pot of gold.

      Rich

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #18
      I believe the 2 valves are for the step and step cover, at least on mine they were.

      Re: Dash Air Stuck on Defrost/Vacuum Pump Replacement

      Reply #19
      You're correct but I think the vacuum generator on mine was fed by a through line from the two valves.  When I went to an electric vacuum pump, I had to cap the line.

      Rich