Foretravel Motorhome Forums => Foretravel Tech Talk => Topic started by: Elliott on December 25, 2020, 09:49:38 pm
Title: How Dash Air Works - U320
Post by: Elliott on December 25, 2020, 09:49:38 pm
I'm getting ready to replace the vacuum pump for the dash air (behind entry step). I understand how a vacuum pump works, and I understand that when there is a failure, the air blows out of the defroster vents only, as a default. So when the vacuum pump quits working, I get the symptoms I'm seeing. What I don't understand is what a working vacuum pump is actually doing that allows the knobs on the dash to direct air to different vents. I know what I need to do to fix my problem, I just don't actually understand how the system works. Google and FF searches have yielded little results.
Could someone please give me a 1000ft explanation of how the system works? I was under the impression that a vacuum pump is often used to remove excess moisture from an HVAC system but I don't see how that would affect whether or not the system responds to the dash controls.
Bonus points if you can explain why, when installing the new vacuum pump, you simply cap off that line that comes from the right side of the unit.
Title: Re: How Dash Air Works - U320
Post by: craneman on December 25, 2020, 10:05:47 pm
The dash registers have diaphragms that move levers that control where the hvac air is directed. The vacuum pump pulls vacuum on the diaphragms. With no vacuum the default is defroster for safety. My system uses a venturi effect vacuum generator. Air passing by a line going to the vacuum reservoir creates vacuum. If a vacuum pump were to replace it the line would not be needed that the air passes through and would be capped off.
Title: Re: How Dash Air Works - U320
Post by: Woody & Sitka on December 25, 2020, 10:27:03 pm
Elliot, here's how to replace the dash vacuum generator with a diesel vacuum pump:
Dash Air Vacuum Generator (http://web.archive.org/web/20200111053757/http://beamalarm.com/Documents/dash_air_vacuum_generator.html)
Title: Re: How Dash Air Works - U320
Post by: dsd on December 25, 2020, 10:33:12 pm
1 verify power to vacuum pump prior to replacement 2 If you are receiving power verify old vacuum pump is or is not working, finger over open line is enough to tell tone change in pump and actual vacuum 3 If good vacuum at pump it is a control issue, no vacuum and you have power or bad pump.
The system works by having a vacuum source and valves switching were the vacuum goes to open or close diaphragms. Diaphragms are basically like motor actuators using vacuum for power.
System needs to be in good condition because of low volume pump, leaks will cause system to cycle back and never fully operate/close. Old lines, diaphragms, pumps, valves can be problematic Start T/S at power then pump to thru system. I single failure anywhere will cause poor or no operation of the system this is not the kind of vacuum pump used to evacuate your Freon system. This is control of your HVAC controls Scott
Title: Re: How Dash Air Works - U320
Post by: craneman on December 25, 2020, 10:33:35 pm
Title: Re: How Dash Air Works - U320
Post by: Elliott on December 25, 2020, 10:50:19 pm
Thanks guys. The pump isn't turning on at all so I'll check that it's getting power before I go replacing the whole thing.
To that note, when inspecting the two electrical terminals coming from the new pump, there is nothing indicating whether or not one is negative and one is positive. In order for the compressor to work in the pump, I thought the motor needed to spin the rotor in the right direction to create a low pressure system that moves air from the suction port to the exhaust valve. Is it not important to apply the positive and negative wires to the correct terminals to achieve this?
If yes, how do I determine which wire goes to which terminal? Both wires are black.
Title: Re: How Dash Air Works - U320
Post by: dsd on December 25, 2020, 11:15:46 pm
I would think they would be polarity sensitive. My dash was also not working and it was not getting power. Found a crushed wire under coach. I seem to recall they were different colors and like a number 12 wire. Scott
Title: Re: How Dash Air Works - U320
Post by: oldguy on December 26, 2020, 12:02:14 am
I had to change the vacuum hose that came out of the vacuum motor as the ends of the hose wouldn't seal any more.
Title: Re: How Dash Air Works - U320
Post by: craneman on December 26, 2020, 12:15:28 am
Thanks guys. The pump isn't turning on at all so I'll check that it's getting power before I go replacing the whole thing.
To that note, when inspecting the two electrical terminals coming from the new pump, there is nothing indicating whether or not one is negative and one is positive. In order for the compressor to work in the pump, I thought the motor needed to spin the rotor in the right direction to create a low pressure system that moves air from the suction port to the exhaust valve. Is it not important to apply the positive and negative wires to the correct terminals to achieve this?
If yes, how do I determine which wire goes to which terminal? Both wires are black.
Did you look closely at the pump to see if the + and - are marked? Curious if all the vacuum motors that I see posted were originally the same vacuum generator I have and have been upgraded.
Title: Re: How Dash Air Works - U320
Post by: hdff on December 27, 2020, 02:03:14 am
Here is a pic of the vac pump assembly that I built to replace the vacuum generator. Worked well. Amazon.com: Dorman 904-214 Electrical Vacuum Pump for Select Ford/Dodge... (https://www.amazon.com/Dorman-904-214-Electrical-Vacuum-Select/dp/B001KQF6PC/ref=asc_df_B001KQF6PC/?tag=hyprod-20&linkCode=df0&hvadid=312462950315&hvpos=&hvnetw=g&hvrand=13260899758493756616&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9027799&hvtargid=pla-493903279818&psc=1&tag=&ref=&adgrpid=70635887228&hvpone=&hvptwo=&hvadid=312462950315&hvpos=&hvnetw=g&hvrand=13260899758493756616&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9027799&hvtargid=pla-493903279818)
Elliott, it may be just a bad vacuum switch,,,,,,,,,,,,,,,, here is a link to my post when I replaced mine
Vacuum switch for dash AC controls. (https://www.foreforums.com/index.php?topic=34465.0)
Title: Re: How Dash Air Works - U320
Post by: Elliott on December 27, 2020, 03:12:25 pm
Thanks guys, this is all great stuff. The HOA we're at right now is rather up tight so I've had to be sneaky when working on the rig. I was able to confirm that I'm getting 12v at the wires, and I was able to source a 1/4" plug to cap the air line off at the T behind the step. Now I just need to find a place to get it done and test it.
One thing I have noticed is that despite setting the knob to "AC" or "Max AC", it still only blows hot. Could this also be a symptom of the bad pump or does it indicate I also have an issue with the air conditioning unit on the M11?
Title: Re: How Dash Air Works - U320
Post by: craneman on December 27, 2020, 03:22:59 pm
Turn on the A/C and see if the A/C compressor is working. Probably not and that would be the problem.
Title: Re: How Dash Air Works - U320
Post by: oldguy on December 27, 2020, 03:30:28 pm
If low on Freon the compressor won't work. That is the first thing to check. If the compressor is seized the belt would be broken,
Title: Re: How Dash Air Works - U320
Post by: John44 on December 27, 2020, 03:39:02 pm
On the 96 you have to turn the switch to AC,turn the fan on and turn the temperature controller all the way to the left for the coldest.
Title: Re: How Dash Air Works - U320
Post by: Journey, Roam, Explore on December 28, 2020, 01:10:54 pm
I've been experiencing AC problems for a while. When I was at Xtreme last month I was told that my vacuum pump was rusted out and probably no good. I have a dorman vacuum pump being delivered in the next few days and when replace it when I get out to Arizona. I'm not sure if that will fix the problem but that will be step one. after that I'll take it to an AC place and let them fiddle around with it. I also think I need to replace the dash controls but have done little to research that one yet I figure I'll try the vacuum pump first. Good luck in your troubleshooting I feel your pain when it comes to the homeowners association. best thing we ever did was when we sold the house. Got rid of the homeowners association may they rot in hell... Well maybe not that but I would never buy a place with a home association again.
Title: Re: How Dash Air Works - U320
Post by: WS6_Keith on May 03, 2021, 03:44:58 pm
What were the original issues/symptoms that led you to the vacuum pump as the culprit?
On my last trip, the dash A/C had some issues. When I turned it on, I heard some clicking sounds, like a relay that was clicking on and off. After sitting for a few minutes, I tried it again and it came back on. Now it's intermittent. While I had the back of the dash off to replace the 2000 Ford radio (haha), I looked at the switches and they aren't in the greatest of shape. I figured given the condition of them, I'd replace these first. Anyone have a source?
(https://www.foreforums.com/imagecache.php?image=http%3A%2F%2Fspeedcraving.com%2FForetravel%2FDash-AC.jpg&hash=c7f1ca28eeb3ede3ad3327b2c69e77b8" rel="cached" data-hash="c7f1ca28eeb3ede3ad3327b2c69e77b8" data-warn="External image, click here to view original" data-url="http://speedcraving.com/Foretravel/Dash-AC.jpg)
Title: Re: How Dash Air Works - U320
Post by: wolfe10 on May 03, 2021, 04:14:32 pm
Inadequate vacuum to the dash HVAC results in air coming out only the defrost vents-- the default position.
Could be a bad vacuum pump, could be something as simple as a vacuum line that has come off.
Certainly, start with the cheap, easy things-- check lines, vacuum canister, etc.
Title: Re: How Dash Air Works - U320
Post by: Travelin' Man (RIP) on May 03, 2021, 04:24:41 pm
VCS should know where to get the switches;
Victory Climate Systems - Climate Control Products for a World in Motion Victory Climate Systems - Climate Control Products for a World in Motion (http://victoryclimatesystems.com/)
Title: Re: How Dash Air Works - U320
Post by: Journey, Roam, Explore on May 03, 2021, 08:17:10 pm
Thanks T-man. Need new switches on mine. I'll call them tomorrow.
Title: Re: How Dash Air Works - U320
Post by: WS6_Keith on June 28, 2021, 03:22:31 pm
I replaced the switches in mine but that didn't solve the issue. When turning the mode switch, I do hear the actuators moving in the dash, but the fan motor is intermittent at best. Turning to Max AC, the engine loads down (AC compressor) and the fan on the condenser starts running, so I know that part is working, but the fan comes on if/when it feels like it. Maybe it's a bad connection or it's a fan.
Anyone have pictures of where the fan is in the dash? I see where all the ducting comes from and it sure looks like if there's a fan in there, it's buried and a bear to get to. I hope I'm wrong.
Title: Re: How Dash Air Works - U320
Post by: TGordon on June 28, 2021, 03:41:34 pm
Quote from: WS6_Keith link=msg=427614 date=1624908151
Anyone have pictures of where the fan is in the dash?
[/quote
I have a U320. My dash HVAC fan is located at the back of the unit, facing towards the front of the coach, in a plastic housing.
Tim
Title: Re: How Dash Air Works - U320
Post by: kepeters on June 28, 2021, 05:55:10 pm
To administrators:
When I want to print a post for future reference I go to the top and click "PDF" in the right corner.
This works fine for presently posted posts, except this one, "How dash air works."
There I receive an error .... 16 bit depth not supported ....
I assume it has something to do with the picture quality in the post.
Advice, please
Regards
Klaus
Title: Re: How Dash Air Works - U320
Post by: WS6_Keith on June 29, 2021, 04:00:58 pm
Thanks TGordon. My blower location isn't readily apparent just by pulling the dash cover off. Any pics of the location?
I also read in another thread about a "bridge rectifier" that could also cause the fan not to run. Does anyone have a picture that shows the location? Any idea how to test or where to buy a replacement?
Title: Re: How Dash Air Works - U320
Post by: oldguy on June 29, 2021, 05:37:36 pm
I have had a blower motor not working and it turned out to be a ground that was riveted to the housing was loose. Hammered it tight and got it working.
Title: Re: How Dash Air Works - U320
Post by: WS6_Keith on June 29, 2021, 10:53:30 pm
I had to move the coach around today and paid specific attention to the AC. I turned it on and it seems that the blower is working, but only on low speed. It's very slow/low, but cold air is coming out. So it seems the blower is working, but not responding to the fan speed switch. The switch is new as of a month ago. What else should I be checking next?
Title: Re: How Dash Air Works - U320
Post by: dsd on June 29, 2021, 11:26:43 pm
In your wiring diagram I'm pretty sure you will see between the switch and the motor a resistance block for your lower speeds. And straight thru for hi speed. Real prone for corrosion issues. May be able to clean up or replace if damaged beyond repair. Scott
Title: Re: How Dash Air Works - U320
Post by: WS6_Keith on June 30, 2021, 11:18:50 pm
I found the 4 wires coming from the switch and followed them down to a large cluster of wires at the center of the dash next to the metal box with the SGM sticker. From there, I can't see where they go without cutting zip ties and such. I also don't see an obvious blower fan location. Here are pics of the inside of the dash...where the heck is this thing? It sounds like it's under the center of the dash. I don't see how that comes off. Any hints?
Title: Re: How Dash Air Works - U320
Post by: craneman on June 30, 2021, 11:34:31 pm
Foretravel changes things all the time, but here is how a '99 works.
dash air expansion valve (https://www.foreforums.com/index.php?topic=27441.msg224665#msg224665)
Title: Re: How Dash Air Works - U320
Post by: Rich Bowman on July 01, 2021, 04:38:29 am
The panel in the last picture is velcro'd on. Pull from the bottom and the top edge is slipped under the top of the dash. Among other things, many self resetting CBs behind it.
Rich
Title: Re: How Dash Air Works - U320
Post by: Peter on July 01, 2021, 11:35:52 pm
I just started reading this post and realized I was having some of the same issues with my AC. I am not getting very cold air and have tried charging the system. I had a tech look at it and he said I would have to replace this unit and hoses. (See pictures) This unit is on the drivers side right side of engine. Is he correct and how is this part of the AC?
Title: Re: How Dash Air Works - U320
Post by: craneman on July 01, 2021, 11:39:45 pm
That is your A/C drier filter and if the pressure is too high on the highside and too low on the lowside should be replaced. Not the only thing that can cause that but the first thing to replace in trouble shooting.
Title: Re: How Dash Air Works - U320
Post by: Peter on July 01, 2021, 11:43:34 pm
Ok do the hoses have to be replaced as well? Do you happen to know the part number for this and if it is a diy project?
Title: Re: How Dash Air Works - U320
Post by: craneman on July 02, 2021, 12:14:02 am
They might think that the hoses are frozen to the fittings. If they can be removed I don't know why they would have to be replaced.
Title: Re: How Dash Air Works - U320
Post by: WS6_Keith on July 02, 2021, 01:10:28 am
The panel in the last picture is velcro'd on. Pull from the bottom and the top edge is slipped under the top of the dash. Among other things, many self resetting CBs behind it. Rich
Thanks Rich. I did get this panel and the one next to it off...bottom of the dash fully exposed and I still don't see anything that looks like a darn blower! Guess I'm going to have to call the mothership tomorrow.
Title: Re: How Dash Air Works - U320
Post by: Pamela & Mike on July 02, 2021, 05:48:26 am
I also read in another thread about a "bridge rectifier" that could also cause the fan not to run. 1. Does anyone have a picture that shows the location? 2. Any idea how to test or where to buy a replacement?
Keith,
1. Now that you have the dash apart you can see the bridge rectifiers mounted on the metal air box. they are the little square black things with 4 spade lugs. They will be mounted with a screw through the center hole in each one. They are just above the cube relays (one of these may be your culprit rather than the rectifier) that I can see in this last picture you posted.
2. With a multimeter. They aren't anything but a a fancy diode set. Here is the first video I ran across for a simple explanation testing a bridge rectifier with multimeter - Bing video (https://www.bing.com/videos/search?q=testing+a+bridge+rectifier+with+multimeter&docid=608028169337791037&mid=363332C38A62A325D5BE363332C38A62A325D5BE&view=detail&FORM=VIRE) This is easier than me trying to explain in a long post here.
3. The fans are hid inside the metal boxes that you have exposed. You will need a 1# coffee can for all the screws you are about to remove to get to the fan.
Mike
Title: Re: How Dash Air Works - U320
Post by: turbojack on July 02, 2021, 09:23:56 am
I would not worry about getting to the fan motor until you have verify that the fan is getting the correct power. As stated above high speed is just going through a relay to give the motor 12-13 volts. I see this relay go bad all the time due to bad loose connections on the relay.
I would also verify your switch even though you said it was new is working correctly.
Title: Re: How Dash Air Works - U320
Post by: WS6_Keith on July 02, 2021, 10:22:44 am
I would not worry about getting to the fan motor until you have verify that the fan is getting the correct power. As stated above high speed is just going through a relay to give the motor 12-13 volts. I see this relay go bad all the time due to bad loose connections on the relay.
My latest testing seems to show that the fan blows on low all the time. The switch has 3 settings and 3 connections. It looks like the high speed connection has 2 wires going to it. Is this power and the output? What should I see coming out of the switch? I'm guessing it's basically a resistor switch and I'll see 12v on high and lower voltages on medium and low?
Title: Re: How Dash Air Works - U320
Post by: WS6_Keith on July 02, 2021, 11:58:02 am
Are the bridge rectifiers expensive? If not, perhaps I'll just replace them to be sure...I'm sure they are as old as the coach, so old enough to vote. :)
Title: Re: How Dash Air Works - U320
Post by: Pamela & Mike on July 02, 2021, 01:50:35 pm
My latest testing seems to show that the fan blows on low all the time. The switch has 3 settings and 3 connections. It looks like the high speed connection has 2 wires going to it. Is this power and the output? What should I see coming out of the switch? I'm guessing it's basically a resistor switch and I'll see 12v on high and lower voltages on medium and low?
Possible this is the way it is wired. Check with vm and get back to us. Follow the high speed wire to relay and see if relay is working relay should have 12v going to it and then switch is on high should have 12v going out to Motor
Title: Re: How Dash Air Works - U320
Post by: WS6_Keith on July 02, 2021, 05:51:35 pm
I will test this stuff this weekend, but also called FT and ordered 5 new rectifiers. $11 each, so that doesn't break the bank. If there's an issue, I'll have the parts next week. If not, I'll have spares.
Title: Re: How Dash Air Works - U320
Post by: WS6_Keith on July 05, 2021, 12:22:25 pm
I guess I should have looked a bit deeper before just ordering parts. More dash disassembly has revealed no less than 15 of those bridge rectifiers under there. What's also odd is that every video/webpage I've found mentions using all 4 posts to convert AC to DC, but all of these are wired only using the load terminals. I'm not sure what they are doing with only those two terminals in use. There doesn't appear to be any loose wiring in there, and it looks like I'll have to cut apart a few wire ties to separate out the fan switch wires to follow them.
Looking on my schematic, I don't even see these rectifiers shown, or the dash fan speed switch. Maybe my manual is missing a page? I might have to make another call to FT about this tomorrow.