Vacuum Generator finally quit

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Vacuum Generator finally quit

August 04, 2010, 01:38:10 pm

The vacuum generator that operates the from air direction door has been clicking for 5 years. Recently the front air will only work through the defrost outlets so I assume that the generator has finally quit. The last time I checked Foretravel wanted about 300.00 for the part. Anyone replaced or repaired this unit and where.

Re: Vacuum Generator finally quit

Reply #1 – August 04, 2010, 02:56:00 pm

JEG'S PN 884-28149

Volvo's and VW/Audi's also use small 12V vacuum pumps - cheap in junkyards

General Motors installed a 12 volt vacuum pump in their J-car models

(ie: Chevy Cavalier or Pontiac J2000, with the 1.8 liter engine only) in the early 1980's. You may find such a motor at an auto parts retailer or through a GM dealer, or possibly an auto dismantling yard. http://www.readybrake.com/electricvacuumpump.html http://www.summitracing.com/parts/CLP-12VVCP/ google '12V vacuum pump' and go from there...

Quote

Chuck Croft wrote:

The vacuum generator that operates the from air direction door has been clicking for 5 years. Recently the from air will only work through the defrost outlets so I assume that the generator has finally quit. The las time I checked foretravel wanted about 300.00 for the part. Anyone replaced or repaired this unit and where.

Re: Vacuum Generator finally quit

Reply #2 – August 04, 2010, 07:14:41 pm

Chuck, Not sure if the 320 is the same but on the GV's you will find on the firewall a small round puck with vacuum lines going to it. This is the sensor that tells the Vac pump to operate. Before you condemn the pump hot wire it to see if it will run. If so clean the small round puck with brake cleaner etc. If you remove the line from the pump it should run continuously.
YMMV

Dash air problem

Reply #3 – November 27, 2010, 08:47:45 am

The dash air output is stuck on the windshield regardless of where you set the controls. It will not discharge to the dash vents or the floor.
Any suggestions on how to troubleshoot this problem will be appreciated.
Russell
2001 36' U295

Re: Dash air problem

Reply #4 – November 27, 2010, 08:58:20 am

Quote from: Russell Jinks – November 27, 2010, 08:47:45 am

The dash air output is stuck on the windshield regardless of where you set the controls. It will not discharge to the dash vents or the floor.
Any suggestions on how to troubleshoot this problem will be appreciated.
Russell
2001 36' U295

Check the air tank and connection lines in the area behind the flap when the entrance step is extended or the vacuum pump generator.

Re: Dash air problem

Reply #5 – November 27, 2010, 09:25:16 am

The default is defroster when the air flow direction doors do not work. Some doors were moved by electric motors, some were vacuum motors.

Vacuum motors need a source of vacuum, created by air flow or electric vacuum pump.
When vacuum style fails, it could be any hose that is disconnected or circuit breaker open for electric vacuum motor or the motor itself.

Re: Dash air problem

Reply #6 – November 27, 2010, 10:40:08 am

Yup, here is how I would proceed.

Open the front of the coach and locate the vacuum pump. Pull the hose off it. Turn the ignition to ON (don't need to start the engine).

If the pump does not run, check for 12 VDC to the pump. If not there is a relay connected to a vacuum switch that turns the pump on/off. Also a separate fuse.

If the pump runs, then you may have nothing more than a hose that fell off or a hose with a crack in it. Trace the hose to the vacuum switch, vacuum reservoir and on to the dash HVAC.

Brett

Re: Dash air problem

Reply #7 – November 27, 2010, 12:24:10 pm

As they say, you learn something new every day. That sure is true today reading about the Vacuum in the dash and how it seems to also operate the step flap and heater controls.
My coach is in Xtreme shop and I will not get to the coach manual / wiring diagrams until the middle of week, but I sure am going to have a read and learn more about this vacuum pump.

I just wonder why with all the air pressure / supply all around the coach, why they would need a vacuum pump ?

The other interesting thing, the step only comes up when the air pressure reaches about 40 PSI. Aint that interesting ? , psi , not inches of vaccum ?

Gotta learn something new every day, and I thank all for the continuing education.

Re: Dash air problem

Reply #8 – November 27, 2010, 09:41:36 pm

Dave,

Are you suggesting a vacuum line attached to the air compressor inlet? Autos have a vacuum source because of the throttle valve. Since diesels don't have a throttle valve they need some source for vacuum.

Russel,

I had the same problem. In my case it turned out that the 12V relay that powers the vacuum pump had died.

All,

A Mityvac is a good tool to check vacuum issues. I use it to find leaks as well as check vacuum actuated switches.

Re: Dash air problem

Reply #9 – November 28, 2010, 07:11:02 pm

Hi John,
I am not saying anything, I am asking, I am on the way to Nac (currently in Motel 6 in Choo Choo, Tn) to capture my coach from Xtreme this week, then I am gonna get into the manual that came with the coach, mainly the wiring diagrams, as I am looking for this vacuum pump every one seems to be yaking about.
I am hoping, having the 2001, that it does not have this said vacuum pump. Sure am hoping

Like I mentioned, never ending educational device these Foretravels.
As for the Mighty Vac hand pump, you bet, I have the model that you flip the lever and it becomes air pump in addition the the vacuum pump. Very handy lil critter, check lots of things.

Re: Dash air problem

Reply #10 – November 28, 2010, 07:24:31 pm

The vacuum pump that operates the dash ac/heat doors on my U280 is located on the firewall behind the front grill to the left and below the condenser coil. Very easy to check operation, disconnect a hose with key on.

Re: Dash air problem

Reply #11 – November 28, 2010, 07:42:58 pm

Quote from: Dave M – November 28, 2010, 07:11:02 pm

I am gonna get into the manual that came with the coach, mainly the wiring diagrams, as I am looking for this vacuum pump every one seems to be yaking about.
I am hoping, having the 2001, that it does not have this said vacuum pump. Sure am hoping
Like I mentioned, never ending educational device these Foretravels.

Dave,
Here is the vacuum generator you are looking for on the schematic be-2254.

Re: Dash air problem

Reply #12 – November 28, 2010, 07:49:45 pm

My problem was cracked vacuum hoses. Several of them that attached to the ventilation control had to be replaced.

Re: Dash air problem

Reply #13 – November 28, 2010, 08:25:14 pm

Barry,
That's very interesting. So, sometime between 1993 and 2001 Foretravel switched from a electric vacuum pump to a vacuum generator. For those who don't know, a vacuum generator takes high pressure air and passes it through a venturi to create a suction or vacuum. Same principle of how a garden hosed attached Miracle Grow sprayer works. I've used quite a few vacuum generators in my factory automation like. They have no moving parts and are very compact - about the size of an air valve. They have 3 ports: air supply (80-120 psi), exhaust, and suction. The down side is they use more energy (energy to create the compressed air) than a vacuum pump but the upfront cost are much lower. The amount of air used by these is probably very small compared to the amount produced by the engine compressor.

So what it sounds like to me is that if your coach has a vacuum generator - you're going to need some air in the tanks to see you see if your ventilation doors are working.

Quote

I just wonder why with all the air pressure / supply all around the coach, why they would need a vacuum pump ?

The ventilation systems are borrowed from cars which have "free" vacuum from their gas engines. It's just cheaper to add a vacuum pump than redesign a system to work on air pressure. I believe most new cars (and coaches alike) today have switched from vacuum to electric motor actuated ventilation doors. My guess is because electric motors are cheaper and it's easier to integrate into an electronic temperature control system that all the new cars have today.

Also, it looks like the door step and door cover do run off compressed air, not vacuum.

Re: Dash air problem

Reply #14 – November 28, 2010, 08:45:13 pm

Dave,

Don't push that F150 too fast. I know you are anxious to see the latest masterpiece from Xtreme. When you drive home, pretend that all those people are not admiring your home on wheels.

Re: Dash air problem

Reply #15 – November 29, 2010, 01:05:02 am

Barry, John and George,
Many thanks for the info and most interesting, I feel at a disadvantage cuz the coach and manual ain't here, but I soon will get into this Lil feature.
John, I see we are on the same view on the compressed air vs vacuum.
The amazing part, the step flap only closes once the air pressure up to about 30-40 psi, I have never heard a electric motor humming anywhere in the dash area.
Like I been saying I am gonna get into this Lil jewel. Fascinating subject.
George, hope all em rubber neckers keep their wheels between the lines.

Re: Dash air problem

Reply #16 – November 29, 2010, 12:46:35 pm

I am sorry to hear about the switch to a vacuum generator. A downside to the generator is the need to have the engine running. There have been a few occasions when I wanted to use the dash air fan while working on the dash and I was able to do so without running the engine. On some vehicles I have seen vacuum reservoirs to hold vacuum when the vacuum pressure is low. Does the vacuum generator have a reservoir?

Re: Dash air problem

Reply #17 – November 29, 2010, 03:39:07 pm

John,
I had a chat with James T. today concerning the vacuum issue. I think I was told all Foretravels use vacuum to control the dash vents, some use the air operated vac pump and the newer ones have an DC pump. I am not fully exactly sure of all this, but that seemed to be the final verdict. No real clear cut answer. No idea of what newer means. Phenix has the DC pump.
As I said I see I will have to get into my manual, then get my eyeballs on the subject under the steps etc. Something I really need to find out.
Always more questions than answers, sorta normal.

Re: Dash air problem

Reply #18 – November 29, 2010, 07:06:18 pm

I had the same problem of air only to the defrost vents. On my 96 U270 the air diverter doors are operated by small electric motors. There is a relay circuit board with 3 relays to control the motors. The relays reverse the polarity to the motors to drive them in the opposite direction. There is always dc electrical power going to the motors when the key is on. The motor stops when the door is open or closed and apparently the motor can take it as they don't burn up. In my case the relay board was bad and had to be replaced. Foretravel had it, and I could not locate it or the relays anywhere else. The motors can be tested by isolating them electrically (remove the wires which are soldered on or unplug from the circuit board) and applying 12 vdc and reversing the connection to check that they work in both directions. The only thing on the relay circuit board besides the 3 relays are 3 small resistors and 2 connections for the wiring (1 for the motors and 1 to the controls on the instrument panel). Other Foretravels may be different.

Re: Dash air problem

Reply #19 – November 29, 2010, 08:34:49 pm

Quote from: Jerry Whiteaker – November 29, 2010, 07:06:18 pm

I had the same problem of air only to the defrost vents. On my 96 U270 the air diverter doors are operated by small electric motors. There is a relay circuit board with 3 relays to control the motors. The relays reverse the polarity to the motors to drive them in the opposite direction. There is always dc electrical power going to the motors when the key is on. The motor stops when the door is open or closed and apparently the motor can take it as they don't burn up. In my case the relay board was bad and had to be replaced. Foretravel had it, and I could not locate it or the relays anywhere else. The motors can be tested by isolating them electrically (remove the wires which are soldered on or unplug from the circuit board) and applying 12 vdc and reversing the connection to check that they work in both directions. The only thing on the relay circuit board besides the 3 relays are 3 small resistors and 2 connections for the wiring (1 for the motors and 1 to the controls on the instrument panel). Other Foretravels may be different.

Where are the motors and the relay circuit board on your coach?

Re: Dash air problem

Reply #20 – November 29, 2010, 09:35:38 pm

Quote

I had a chat with James T. today concerning the vacuum issue. I think I was told all Foretravels use vacuum to control the dash vents, some use the air operated vac pump and the newer ones have an DC pump. I am not fully exactly sure of all this, but that seemed to be the final verdict. No real clear cut answer. No idea of what newer means. Phenix has the DC pump.

Dave M,
If James says so, it's so. The term above "air operated vac pump" is, I believe, another name for what I am calling a vacuum generator. It sounds like Foretravel used the vacuum pump (which on my '91 is 12volts DC) then changed to a vacuum generator (per Barry diagram for an '01) and then they went back to a vacuum pump (per what James said above for the Phenix). I only made the assumption the newer coaches were all electric vent door drive based on the trend seen with automobiles - I was only guessing. I remember buying a new Acura in 1989 and the new electric ventilation controls was one of their new features they boasted about. Apparently vacuum controls are still alive and well in new vehicles. I find it fascinating learning about how other engineers decide to design things - I was always one of those kids who took things apart to figure out how they worked. And I still do it today.

Re: Dash air problem

Reply #21 – November 30, 2010, 11:28:12 am

Quote from: ncaabbfan – November 29, 2010, 08:34:49 pm

Where are the motors and the relay circuit board on your coach?

They are on the sheet metal box under the dash where all the vent hoses are attached. Open the hood in front of the instrument panel, remove the screws at the bottom of the 2 hinges and remove hood. The part in front of the snack table is hinged and lifts up. Can't remember if I removed that, but probably did. The long flat padded dash is held in place with velcro and can be removed by lifting up (be careful as it is very thin plywood and may break if bent). Also the round vents have to be disconnected. At this point you may have to remove the padded vertical piece in the middle (held in place with screws) in order to get to the metal box. The metal box is held together with screws and you may have to take off a panel or two to see all the motors. I suppose everyone knows about the circuit breakers behind the panel above the steps. Grab the bottom and pull aft to open.

Re: Dash air problem

Reply #22 – November 30, 2010, 11:31:14 am

Quote from: Dave M – November 29, 2010, 03:39:07 pm

I had a chat with James T. today concerning the vacuum issue. I think I was told all Foretravels use vacuum to control the dash vents, some use the air operated vac pump and the newer ones have an DC pump. I am not fully exactly sure of all this, but that seemed to be the final verdict. No real clear cut answer. No idea of what newer means. Phenix has the DC pump.

Our '03 had the air-operated vacuum generator, which failed maybe 1 1/2 years ago. No more parts available, so Steve had to install the DC pump as a retrofit. Noisy little bugger and rather pricey for what you get.

Michelle

Re: Dash air problem

Reply #23 – November 30, 2010, 04:22:35 pm

Quote from: Jerry Whiteaker – November 30, 2010, 11:28:12 am

Quote from: ncaabbfan – November 29, 2010, 08:34:49 pm
Where are the motors and the relay circuit board on your coach?

They are on the sheet metal box under the dash where all the vent hoses are attached. Open the hood in front of the instrument panel, remove the screws at the bottom of the 2 hinges and remove hood. The part in front of the snack table is hinged and lifts up. Can't remember if I removed that, but probably did. The long flat padded dash is held in place with velcro and can be removed by lifting up (be careful as it is very thin plywood and may break if bent). Also the round vents have to be disconnected. At this point you may have to remove the padded vertical piece in the middle (held in place with screws) in order to get to the metal box. The metal box is held together with screws and you may have to take off a panel or two to see all the motors. I suppose everyone knows about the circuit breakers behind the panel above the steps. Grab the bottom and pull aft to open.

Interesting....I will have to check into this some next time I am at the MH. I will probably have some "dumb" questions after I check our MH. Thank you.

Re: Dash air problem

Reply #24 – November 30, 2010, 06:35:24 pm

I just had to change mine too. I changed it to the DC vacuum pump and you will hear it if you turn the key and have the door open and say, wow what is that noise. Once you are started though you do not hear anything. Mine was under the front step behind the flap.

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