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 (https://www.amazon.com/gp/product/B001KQF6PC/). 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.
- Wiring harness for the pump. (https://www.amazon.com/gp/product/B01D8VLUDS) Part #: 645-740
- A 1/4" male plug (https://www.homedepot.com/p/Everbilt-1-4-in-MIP-Brass-Plug-Fitting-802379/207176376), to cap the air line. Part number: LFA-737 and Teflon tape
- 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.
- Turn ignition on and test the dash air by fiddling with the knobs
[/list]
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?
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
This is how my set up looked. Keeps your pump from running as much
Keith
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
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
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
Mine was behind the fold down entry step.
Rich
That's the way our 320 was but here's what it looks like on this one.
jor
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
Was this directed at me (jor) or Joe from Keith & Joe? If me, that's the question. Where's the pump?
jor
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?
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
Mine is in front behind the lights on the passenger side I believe.
JOR - Those two valves control the step and the vacuum generator. Follow the air lines to the pot of gold.
Rich
I believe the 2 valves are for the step and step cover, at least on mine they were.
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
There is a 1/4" air line that runs from the step/step cover valves to the front (left) air tank. That one is indicated on the air schematic. I still can't find this pesky vacuum generator. I thought I knew what everything is on this thing but how about this? What is it? It's above and forward of the ride height valve. Thanks.
jor
jor - If I remember correctly, the vacuum generator on mine was about a 4" cube, made of sheet metal covering the actual vacuum generator. It had an air supply line and a vacuum line attached.
Don't recognize the item in your picture.
Rich
I believe it will also need to have two 12v wires attached to activate a solenoid that controls the incoming air from the air line.
That describes what I removed years ago. After removal, I dissected it as is my usual habit. It was very simple inside, no moving parts. Replaced it with a 12 volt vacuum generator.
Richard
All I did was replace the check valve inside the box, still going.
obsolete vacuum generator (https://www.foreforums.com/index.php?topic=27357.msg223782#msg223782)
Craneman,
I probably should have done the same as you. However, I had already bought a 12 volt vacuum generator and I destroyed the metal box which contained the guts of the original vacuum generator.
Richard
Elliott and hdff
I did this today, thank for the write up. When I turned on the ignition, it was a whomp whomp coming from the pump. How does your sound? Mine did not sound right, I wonder if I got a bum pump?
Side note, the fitting on the back side that has the air hose has been a bear to remove. I had to take the regulator off, put it in a vise and I still cannot remove it with a pipe wrench,, guessing the PO put on some loctiite or something. I will try more tomorrow. Not that I am too disappointed, the regulator gauge is shot so I am going to replace regualtor too. I am chasing an air leak so hope a new regulator may fix it.
Regarding the womp womp: no. Mine is a constant fast waaaaa. Like an air compressor.
Check the air cylinder that moves the step cover too. It's known to leak where the arm exits the tube. I'm getting ready to put a solenoid in line to those regulators you mention because that whole corner of the coach is known to be problematic
Thanks Elliot. I looked at this again. Between the hose going from the pump to the new Dorman amplifier, I put in the check valve that hpff showed. This caused womp womp. With it removed, the pump ran like a compressor for a time, then cycled off and on as it should. I have double checked the valve ensure it is going the right way, but I am confused why the valve would do this? Is a check valve needed?
I will be looking forward to when you do the solenoid!
My vacuum pump was shot so I have a new one. My problem is one of the control
valves is leaking. Does anyone know what they are out of.
If you have the slider on the heater/AC control, the leak may be when the slider is in the far left position. I put a small stop on ours so it blocks the last quarter inch. Otherwise, the vacuum pump ran all the time.
Pierce
I have found the control valve that is leaking and it leaks most in the defrost position.
The pump doesn't run steady. It burps about every 5 seconds. So I would like to
know if anyone knows other equipment that they were installed in.
FOT had both the actuators and the solenoid valves in stock.
Rich
Thanks Rich if I can't find it locally I will try Foretravel.
You probably already know this, but just in case, I have had good luck searching for mystery coach components by:
1. Removing the component and seeing if it has ANY kind of ID number.
2. If ID number present, searching that number with Google.
3. If ID number missing, doing a Google search for the best physical description I can come up with, for instance:
"vacuum heater control valve".
4. When Google returns results of search, go to the "Images" category, and compare the pictures to what you have on hand.
5. You may not hit gold on the first pass, but you can always refine your search parameters and try again. It often works for me!
vacuum heater control valve - Google Search (https://www.google.com/search?q=vacuum+heater+control+valve&tbm=isch&ved=2ahUKEwi7me7r8IH1AhXFfqwKHaToCfcQ2-cCegQIABAA&oq=vacuum+heater+control+valve&gs_lcp=CgNpbWcQARgBMgQIABBDMgUIABCABDIGCAAQCBAeMgYIABAIEB46BAgAEB5Qsg1Y0hhg0zBoAHAAeACAAZIBiAHjB5IBAzQuNZgBAKABAaoBC2d3cy13aXotaW1nwAEB&sclient=img&ei=v5fIYfu9FcX9sQWk0ae4Dw&bih=887&biw=1917&client=safari)
Thanks Chuck, there is a number 2-27106 but I couldn't find anything with it. I went
through what you sent, no luck. I'm trying to find what I need in Canada as the courier
companies are charging big brokerage fees. I paid more for shipping on something I
bought than I did for the item. When the border is stable I will go back to shipping
items to Point Roberts and go there to pick up the items.
Post a few sharp photos of the doohickie, and also the front view of your A/C/heater control panel. I'll try my luck at searching.
I found a photo of the climate controls on a '99 U320 (see below). Is this the same as your coach?
I was looking around online and found reference to Evans Tempcon being the manufacturer for many RV climate control systems. Found the website linked below. The photos of the control panels they sell show control knobs that look very similar to the ones in the photo.
If you don't have luck anywhere else, you might try contacting Comfort Air to see if they can help with parts or information.
HVAC Control Panels - Evans Tempcon - Comfort Air Inc. - (https://comfortairgr.com/product-category/evans-tempcon-motorome-rv-parts/hvac-controls-evans/)
Chuck the second picture is the item I am looking for.
I downloaded this and refer to it often https://www.foreforums.com/index.php?action=media;sa=album;in=593 it's the parts manual for a 2000 and 2003. Your 99 will most likely be the same as the 2000.
Look at page 252-253, it's section 1280 .
I'm having a similar issue where sometimes I can turn the A/C on and it will come out of the dash but after some time, it will switch to the defrost or floor on it's own. Sometimes I can turn it on and it won't go to the dash, only defrost or floor.
It looks like I have the same setup that Elliott posted. Mine is mounted to the passenger side of the generator box. Today I pulled the check valve out and put it on my Mighty Vac. It will hold 15in-Hg for 15 mins, so I'm thinking it's good. Next I connected the Mighty Vac up to the vacuum canister and pulled 18in-Hg on it. It held that for at least 10 mins. Then I connected the Mighty Vac to the vacuum pump and let the pump run (key on). It was able to generate about 14in-Hg of vacuum, so I don't think my issue lies in this system.
Next I'll have to pull the dash apart and see if I have a leak in one of the lines from the solenoids to the dash vents. Maybe the line from the dash control solenoid to the actuator is leaking.
Does it sound like my reasoning is sound?
Thanks Jason for the manual. The 2000 has 3 of the valves where the 1999 uses
4. I have downloaded the manual onto my labtop so thanks for it. I can never have
too many manuals.
Keith if you hold the vacuum in all the control valve switch, it could be an electrical
problem.
Old guy - your second picture is the solenoid valve.
Yes Rich and I have 4 and one of them is leaking. If I can't find a replacement in
Canada I will try Foretravel when I think the border is stable. I can live with just
the defroster working. I have a few other things that I need from Foretravel too.
Got the dash opened up and did some poking around. Vacuum holds fine...turns out I appear to have a vacuum solenoid on the fritz. It works intermittently, even though 12V is applied when dash air is called for. Now I need to figure out where I can get one of these little guys. Any ideas guys?
"Where to get a solenoid?" That's been the subject under discussion for the last 3 days. Go back and start reading this thread from Reply #29.
As Rich said try Foretravel
Foretravel has a replacement. It's not the same as the original and may need to be mounted differently, but it is available for $25 each. Ordered one this morning from Brad.
Thanks Elliott for the write up. Did this update with very little effort and works perfectly.