DAsh HVAC woes again

Topic: DAsh HVAC woes again (Read 1281 times) previous topic - next topic

DAsh HVAC woes again

May 01, 2014, 08:15:28 pm

OK, I find I have no vacuum in the lines. I can't find the vacuum pump. Does anyone know where it is in an '89 U280? Thanks.

Re: DAsh HVAC woes again

Reply #1 – May 01, 2014, 08:22:58 pm

If I remember correctly, think the vacuum pump is in the front area behind the grills. The earlier coaches had a venturi type, It may be mounted fairly close to the ac condenser

Re: DAsh HVAC woes again

Reply #2 – May 01, 2014, 08:53:21 pm

That's what I thought but I'n not seeing anyhting that looks lime a pump there. I'll look again though. It wouldn't be the first time I haven't seen something in plain sight...

Re: DAsh HVAC woes again

Reply #3 – May 01, 2014, 08:55:25 pm

If you can locate the little vacuum reservoir and then follow the lines should be able to find the pump.

Re: DAsh HVAC woes again

Reply #4 – May 01, 2014, 09:11:39 pm

Quote from: red tractor link=topic=21081.msg155859#msg155859 date=139899212
If you can locate the little vacuum reservoir and then follow the lines should be able to find the pump.
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I tried to follow a vacuum line to a reservoir once. I found a gaping cavity under/behind the front bumper that the line dangled into... The vehicle owner had no clue what happened to it...
Here's your sign

Re: DAsh HVAC woes again

Reply #5 – May 01, 2014, 09:25:14 pm

A line from the spherical vacuum resevoir goes to a small metal thing that has big lines running to what may very well be things like airbags. I'll take pix later. mystery mystery...

Re: DAsh HVAC woes again

Reply #6 – May 01, 2014, 09:42:18 pm

Jay ---- On our 91GV the vacuum pump is on the driver's side a little center of the headlight. I raise the hatch on the driver's side and look straight down and it is mounted towards the bottom of the AC condenser and outboard of it. Have fun and have a great day ---- Fritz

Re: DAsh HVAC woes again

Reply #7 – May 01, 2014, 10:12:31 pm

Thanks for answering a question I had. When the mobile tech was looking at the coach, he asked about the vacuum pump that was running, and I said I didn't know what it was for. Now I do.

Re: DAsh HVAC woes again

Reply #8 – May 01, 2014, 10:24:38 pm

Well heck. They must have changed things between '89 and '91. No hardware anywhere near the headlights. The mystery widget on the other end of one hose from the vacuum resevoir is a manifold with no wires goi g to it. The other hose disappears into a harness and dives into the firewall. Hmm. Doesn't match a pump description to me...

Re: DAsh HVAC woes again

Reply #9 – May 01, 2014, 10:38:42 pm

I believe it should be similar to a electric Ford vacuum pump

Re: Dash HVAC woes again

Reply #10 – May 02, 2014, 11:11:34 am

OK, here's my vacuum resevoir, and whatever the thing is that isn't a vacuum pump at the other end of the hose. Going through my Atwood manual, is shows a tiny item on the bottom of the airbox, rioght near the fresh air flapper door, that says it's a vacuum motor... but there's nothing there. Certainly nothing that is a pump of any sort. before it gets hot outside, i'll crawl around under trhere some more, and look in the engine bay just in case this rig uses vacuum from back there somehow.

Re: DAsh HVAC woes again

Reply #11 – May 02, 2014, 12:41:08 pm

Jay,
I think you might be confusing the air system with the vacuum system. Vacuum reservoir is only about 4" in diameter, plastic and spherical. Our coaches might be different but on mine (1991) there is a vacuum pump on the drivers side and behind the bumper. Vacuum reservoir is on drivers side too and visible through the access door that's below the windshield.

Re: DAsh HVAC woes again

Reply #12 – May 02, 2014, 04:48:40 pm

A vacuum 'motor' can be an electric motor/pump OR it can be just a simple air pressure hose that creates a vacuum by blowing over a small venture hole.
AIR-VAC Air Venturi Pumps

Re: DAsh HVAC woes again

Reply #13 – May 02, 2014, 05:05:25 pm

I suspect that's what I have here. The line from the resevoir goes to that thing in the 1st pic. No vacuum there but there is pressure in the incoming line so I bet that's the problem. I'll replace it with either anither venturi pump or a 50 buck electric.

Re: DAsh HVAC woes again

Reply #14 – May 02, 2014, 09:51:30 pm

You are correct in that the thing with the pressure line and the line to the reservoir is what is supposed to make vacuum. On the earlier coaches the park brake had to be released to allow pressure to the venturi to make the vacuum. You can use an electric vacuum pump which should have a switch to shut off the pump when it reaches a certain level of vacuum.

Re: DAsh HVAC woes again

Reply #15 – May 02, 2014, 10:22:23 pm

Golly. Ya know what? I've been chasing this problem whilst parked.... with the brake on! Well guess who's just going to go do a lil experiment...

Thank you... I love this forum. Vacuum controls work. Since I'd taken the venturi pump apart and cleaned it and taken the airbox apart and replaced some foam on the baffles, AND got clued in that nuthin works til pbrake is off, we now have some air coming out the dash vents and pushing button makes things actually happen. Not much air and not much cold but I still call it a win. Next up, see if ac circuit needs a refrigerant rechrge. Guessing yes!

Re: DAsh HVAC woes again

Reply #16 – May 04, 2014, 07:31:34 am

Once again the forum members have come shining through

(not the least bit surprised).

Larry

Re: DAsh HVAC woes again

Reply #17 – May 19, 2014, 07:49:15 pm

To briefly hijack this thread. Does anyone know what the replacement for that vacuum pump would be? I have a '91 GV, the exact same setup as the pictures in this thread, but I am fairly certain that my pump is gone.

Thanks

Dave

Re: DAsh HVAC woes again

Reply #18 – May 19, 2014, 10:40:34 pm

The most technical terrm I've found for it is "venturi vacuum generator". But you might just try taking it apart and cleaning it and givig it a bit of silicone lube and see if it behaves any better. I was happy to find I didn't need to go shopping for a new one as it is my guess that they are no longer stocked. The other thing you might try, first, because it's ever so much easier,' is start the coach, chock the wheels and release the park brake, and just pull the line from the vacuum resevoir that goes to the generator. Hopefully you have vacuum there so that all you have to do is chase down a leak or two.

Re: DAsh HVAC woes again

Reply #19 – May 20, 2014, 12:20:54 am

Quote from: DaveLarose – May 19, 2014, 07:49:15 pm

To briefly hijack this thread. Does anyone know what the replacement for that vacuum pump would be? I have a '91 GV, the exact same setup as the pictures in this thread, but I am fairly certain that my pump is gone.
Thanks
Dave

Attached is a spec sheet I had saved off sometime ago. It's the only 12 volt vacuum unit listed on the sheet. You might try to take it apart to see why it's not working. They might sell rebuild kits and/or motor brushes.
Others have used a Ford unit: Dash Air Vacuum Generator
Here's another post on the subject: vacuum pump

Re: DAsh HVAC woes again

Reply #20 – May 20, 2014, 02:26:37 am

Thanks for the tips John and Jay!

Dave

Re: DAsh HVAC woes again

Reply #21 – May 20, 2014, 09:50:30 pm

The dash AC vent control system quit working last fall as we returned to Tucson for the winter. All the cold air came out of the two vents on top of the dash and not the vents on the front. I found the venturi vacuum generator on the front passenger side of the coach... about a foot or so back from the front. It did produce a vacuum. Also checked the vacuum reservoir, which is basically a "tin can" and found that it held a vacuum. So I gave up on fixing it until we got to Nac. Thought it might be something other than the vacuum. But then as we drove north in Arizona on our 2014 summer trip, cold air started coming from the dash. It had healed itself! Really glad we got the "self healing" Foretravel warranty when we bought the coach.

Jeff Savournin replaced his venturi vacuum generator on his 2002 U320 using an electric vacuum pump he got from FOT. Looked like an easy swap. I don't recall the price, but it was not a bargain.

Re: Dash HVAC woes again

Reply #22 – May 31, 2014, 04:42:03 pm

Hi, so I just completely rebuilt the Gast vacuum generator/pump. Runs perfectly now.

I reinstalled it, and hooked it up, and now all my vent gates pen and close as they should (Yay!), but the pump doesn't appear to ever turn off. Where might the problem lie..? If I unplug the lead from this little, pictured, device, the motor shuts off.

Thanks

Dave

Re: DAsh HVAC woes again

Reply #23 – May 31, 2014, 04:52:49 pm

Disconnect the vacuum line on the coach side of the switch. Block it off with our finger.

If pump continues to run: If strong vacuum present, bad switch. If weak vacuum, bad pump.

If it turns off as it should, keep working toward the dash HVAC to locate leak.

Brett

Re: DAsh HVAC woes again

Reply #24 – May 31, 2014, 11:58:45 pm

What's shown in the picture is the vacuum switch to turn off the pump when it's reached enough vacuum. You either have a leak in one of the lines or this switch is not shutting off like it should. I've found the tubes can crack and leak on the ends where they stretch over a barb - especially on the spherical vacuum reservoir - just nip off an inch and re-insert. If it's the switch its worth fiddling with to see if you can free it up to start working again. If memory serves me, there's a very small slotted screw to adjust the pressure (or vacuum in this case).

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