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
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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.
- Turn ignition on and test the dash air by fiddling with the knobs
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Topic: Dash Air Stuck on Defrost/Vacuum Pump Replacement (Read 2674 times)
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