Re: In Dash HVAC Duct Selector Kaput Reply #25 – July 13, 2016, 11:49:15 pm I'm speaking to other future readers as well as the original post. At some point after you diagnose the vacuum problem you may discover that your electric vacuum pump doesn't work and a replacement is really expensive and no more durable than the one Foretravel used when they built your coach. If you look at your air brakes diagram you may notice that some older models of your coach used an air powered vacuum pump shown there on the diagram. Those air powered vacuum pumps are just a venturi with no moving parts. They're very inexpensive ,should last forever, and use very little air. The diagram probably shows a "safety" (60 psi check valve) and perhaps a solenoid valve that opens when the ignition switch is turned on. I don't feel like digging out my diagram right now unless someone finds this information useful, in which case please say so and I'll do a little research. When my expensive electric vacuum pump dies again I'm putting an air powered pump in for a permanent replacement. I'll probably use an automobile air conditioning service type vacuum pump designed for evacuating the AC system before charging it with refrigerant. I haven't actually done this so proceed at your own risk. Someone on this forum found an air powered vacuum pump from an older Foretravel and installed it in their coach a while back and it worked great. I forget who it was but maybe they'll write in and say where they found it. Quote Selected
Re: In Dash HVAC Duct Selector Kaput Reply #26 – July 14, 2016, 09:15:55 am Quote from: RRadio – July 13, 2016, 11:49:15 pmI'm speaking to other future readers as well as the original post. At some point after you diagnose the vacuum problem you may discover that your electric vacuum pump doesn't work and a replacement is really expensive and no more durable than the one Foretravel used when they built your coach. If you look at your air brakes diagram you may notice that some older models of your coach used an air powered vacuum pump shown there on the diagram. Those air powered vacuum pumps are just a venturi with no moving parts. They're very inexpensive ,should last forever, and use very little air. The diagram probably shows a "safety" (60 psi check valve) and perhaps a solenoid valve that opens when the ignition switch is turned on. I don't feel like digging out my diagram right now unless someone finds this information useful, in which case please say so and I'll do a little research. When my expensive electric vacuum pump dies again I'm putting an air powered pump in for a permanent replacement. I'll probably use an automobile air conditioning service type vacuum pump designed for evacuating the AC system before charging it with refrigerant. I haven't actually done this so proceed at your own risk. Someone on this forum found an air powered vacuum pump from an older Foretravel and installed it in their coach a while back and it worked great. I forget who it was but maybe they'll write in and say where they found it.My '99 still uses it and I posted a thread about repairing it "obsolete vacuum generator" There are also posts about cheap vacuum pumps around $50 to replace vacuum generators. Quote Selected
Re: In Dash HVAC Duct Selector Kaput Reply #27 – July 14, 2016, 07:31:36 pm Quote from: craneman – July 13, 2016, 08:44:33 pmIf you can get air pressure up over 100 psi. and take the line off the vacuum can to the dash see if there is vacuum coming out of the port on the can. If so the generator is working.C-man,Pulled that line off yesterday ............Nada. Quote Selected
Re: In Dash HVAC Duct Selector Kaput Reply #28 – July 15, 2016, 08:25:35 am I'm presently online via wifi which seems reliable. If I can hear air escaping from inside the black boxthen I would say that the problem is there and not further down the line. When the vacuum line from the canister to the dash is disconnected there is no vacuum. Quote Selected
Re: In Dash HVAC Duct Selector Kaput Reply #29 – July 15, 2016, 09:34:11 am I guess a broken vacuum line in the box could be the problem. My problem was not the same, the air never stopped but I had vacuum. Without a check valve as soon as the vacuum switch shut off the solenoid the vacuum would leak out through the generator. Without proper tools to check vacuum it is a tough job. There is a tool called Mighty Vac that maybe Auto Zone or O'Reilly's will loan out. Hook it up to the line to the dash, pull vacuum and see if it holds. If it does you are good from the vacuum canister to the dash. Opening the box up would be something you can do for a visual. 4 screws held mine down and other fasteners held the cover on. Quote Selected
Re: In Dash HVAC Duct Selector Kaput Reply #30 – July 15, 2016, 11:29:55 am I was able to get the black box off and removed 2 screws from the back that seated into the air linefitting. But in order to get the cover off I think the fitting itself has to be taken apart as it encapsulatesthe side of the box. I did get a peek inside and it looks like it could be a pump rather than a venturi. However all the plastic pieces are milky white and not black like any pictures I have seen.Before I took it off the only time I could hear a leak was when the HVAC was turned on. After I R&R'd it,it leaked even with the ignition off, so I disconnected the weather-tight connector and it quit.I didn't dare mess with the air line fitting for fear of having an unstoppable leak, so for now I have the connector ends taped up, and no apparent leak anywhere. Afterthought; I have never heard anything running like a vacuum pump, and with air lines running to the box it must be a venturi rig? Quote Selected
Re: In Dash HVAC Duct Selector Kaput Reply #31 – July 15, 2016, 12:24:03 pm If it has an air line it is a venturi vacuum generator. The power to the solenoid to let the air pass was activated by my ignition and HVAC I was able to lift the cover off without breaking anything. I can't remember exactly but I think there was a nut on the air fitting I took off. Quote Selected
Re: In Dash HVAC Duct Selector Kaput Reply #32 – July 15, 2016, 01:04:41 pm I didn't feel like the box was coming apart withouttaking the fitting apart first. My eyes aren't great but the fitting looked and felt smooth with no wrench flats.When the venturi generator is working properly theair from the system is always exhausting through it whenever the key is on and the HVAC is on, creating an open drain? There is also an adjustable air pressure valve that is probably set to where best vacuum and least amount of air loss are?Thanks C-Man. Quote Selected
Re: In Dash HVAC Duct Selector Kaput Reply #33 – July 15, 2016, 01:33:50 pm Quote from: Traveling Man – July 15, 2016, 01:04:41 pmI didn't feel like the box was coming apart withouttaking the fitting apart first. My eyes aren't great but the fitting looked and felt smooth with no wrench flats.When the venturi generator is working properly theair from the system is always exhausting through it whenever the key is on and the HVAC is on, creating an open drain? There is also an adjustable air pressure valve that is probably set to where best vacuum and least amount of air loss are?Thanks C-Man.There is a vacuum switch that shuts off the air solenoid after vacuum is achieved. You can see it in the post I did. Quote Selected
Re: In Dash HVAC Duct Selector Kaput Reply #34 – July 15, 2016, 02:34:27 pm Quote from: craneman – July 15, 2016, 01:33:50 pmThere is a vacuum switch that shuts off the air solenoid after vacuum is achieved. You can see it in the post I did.I understand, thank you. One more thing. ........... why does my air solenoid stay open whether the ignition switch is on or off,and only close when unplugged? Sticking relay? Quote Selected
Re: In Dash HVAC Duct Selector Kaput Reply #35 – July 15, 2016, 02:44:12 pm It shouldn't. The power comes to the vacuum switch then to the solenoid from the HVAC which I am guessing is only live with the ignition on. Back tracing the power should find out what is feeding it. Quote Selected
Topic: In Dash HVAC Duct Selector Kaput