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| the HVAC designs of Mark Wall [message #333850] |
Fri, 22 June 2018 11:13  |
KB
Messages: 1262
Registered: September 2009
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Hi, I'm currently pondering the cockpit HVAC system, so looking at designs folks have done in the past.
Mark Wall did an interesting presentation in 2006, where he heavily modified the stock AC box, as well as the interior ducts:
https://www.gmcmi.net/wp-content/uploads/2013/02/HVAC-Systems.pdf
He also posted some pictures around 2009 of a very different box configuration, but it looked like a plywood prototype:
http://www.gmcmhphotos.com/photos/hvac-redesign/p30528-hvac-box.html
In the earlier one, he moved the stock blower to the front of the box so it pulls rather than pushes air to reduce the number of bends.
In the later design, he built a flat box with the stock blower on top, pulling air through both the evaporator and heater core at all times
and shooting the air straight through the firewall. I'm curious how that one worked; I'm thinking always going through the heater core might
reduce airflow somewhat, and of course you need a good heater core shutoff.
Does anybody know what Mark finally ended up with?
Getting hot here...
thanks,
Karen
1975 26'
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| Re: the HVAC designs of Mark Wall [message #333869 is a reply to message #333850] |
Fri, 22 June 2018 18:15  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
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I watched Marks earlier presentation I think at the Berrien Springs convention. All good til he got to the 100% recir air part. That doesn't work for me as no ventilation and I like fresh air coming in as I drive. Especially when you have to run in cool rainy weather and get fogging inside because VENT is no longer vent. So you have to run AC and burn more gas wheras the other way fresh air keeps windows clear and you can add heat to it as needed. I have a 77 so I don't think it applies to mine anyway. There was an article by Wes years ago in their news letter about using the dash blower to creat positive pressure in the coach to not draw septic odors in as well. That option is no good with 100%recirc. I want to see if there is a more modern motor/blower like from a 2018 Suburban or Sprinter or something that moves more air less Amp draw. The 90s Caddy's used a flatter design motor probably more efficient as motor tech may have gotten better as Amp draw hurts CAFE.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] the HVAC designs of Mark Wall [message #333883 is a reply to message #333869] |
Sat, 23 June 2018 09:23 |
Russell Mehlenbacher
Messages: 128
Registered: June 2010
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I have Mark's coach... The 100% re-circ is a problem with moisture on the
windshield. We ran thru a thunderstorm and lost 80% of forward visibility
in the temp / humidity swings. In a bit of desperation we wiped, sprayed
anything at hand. Windex does a wonderful job of clearing the glass on a
temporary basis.
The AC does work really well. (except for the moment, compressor reseal
coming soon) The defroster has not done a good job since we took ownership,
I'm finding that the system was stuck together with foam from a can. Time,
vibration and temperature swings have caused a deterioration of defrost
system integrity.
I did get to replace the plywood box lid with a sheet of plastic, probably
PETE. Just something I had in stock. I expect to add some floor vents
(blast doors) for guaranteed fresh air without the noise of the wind wings.
I'm of the opinion that the fastest way to cold air is the addition of
something like the Vintage Air kit.
Russ
On Fri, Jun 22, 2018 at 7:15 PM, John R. Lebetski
wrote:
> I watched Marks earlier presentation I think at the Berrien Springs
> convention. All good til he got to the 100% recir air part. That doesn't
> work for
> me as no ventilation and I like fresh air coming in as I drive. Especially
> when you have to run in cool rainy weather and get fogging inside because
> VENT is no longer vent. So you have to run AC and burn more gas wheras the
> other way fresh air keeps windows clear and you can add heat to it as
> needed. I have a 77 so I don't think it applies to mine anyway. There was
> an article by Wes years ago in their news letter about using the dash blower
> to creat positive pressure in the coach to not draw septic odors in as
> well. That option is no good with 100%recirc. I want to see if there is a
> more
> modern motor/blower like from a 2018 Suburban or Sprinter or something
> that moves more air less Amp draw. The 90s Caddy's used a flatter design
> motor
> probably more efficient as motor tech may have gotten better as Amp draw
> hurts CAFE.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
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--
Russell Mehlenbacher
Rochester Hills, MI
'76 EII
'74 Sequoia
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Russ & Linda Mehlenbacher
Rochester Hills, Michigan
'76 Eleganza
'74 Sequoia
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| Re: [GMCnet] the HVAC designs of Mark Wall [message #333916 is a reply to message #333883] |
Sat, 23 June 2018 20:20 |
KB
Messages: 1262
Registered: September 2009
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Wow, I didn't expect the current owner of Mark's coach to chime in.
What an amazing community! 
He doesn't specify in the first design where he got the intake air from. If you just leave the original blower hole open, it would act as an outside air intake, but unfortunately from directly above the radiator unless you put a duct on it.
I guess he wasn't happy with that design, so changed it again in 2009 or so. The biggest drawback of moving the blower to the front of the box
is you lose all that real estate for mounting the radiator coolant bottle, etc.
If you instead go with a blower in the cockpit, you lose outside air and get more fan noise.
I'm working on some ideas based on his first design which would have at least some outside air as well as recirc, so we'll see how it turns out.
I've already tried other modifications like a bigger recirc opening behind the glovebox, so our poor firewall will be pretty hacked up after this.
thanks,
Karen
1975 26'
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| Re: the HVAC designs of Mark Wall [message #333935 is a reply to message #333850] |
Sun, 24 June 2018 11:27 |
JohnS
Messages: 126
Registered: December 2014
Location: Vacaville, CA
Karma: -2
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Karen, I was watching for the results of the modification you were doing with the blower mounted in the cockpit, but must have missed the outcome. Was noise the main result? Did it cool better? It's pretty hot in my 78 & I too am looking to change things.
John
John Shutzbaugh, Vacaville, CA, ncserv@aol.com;
78 Buskirk stretch, "What were we thinking?"
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| Re: the HVAC designs of Mark Wall [message #333947 is a reply to message #333850] |
Sun, 24 June 2018 19:15 |
JohnS
Messages: 126
Registered: December 2014
Location: Vacaville, CA
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Even though it is a late model coach, I could use MORE air. The temp is ok, just not enough of it.
John
John Shutzbaugh, Vacaville, CA, ncserv@aol.com;
78 Buskirk stretch, "What were we thinking?"
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| Re: [GMCnet] the HVAC designs of Mark Wall [message #333949 is a reply to message #333947] |
Sun, 24 June 2018 20:02 |
powwerjon
Messages: 849
Registered: March 2013
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John,
I would be checking the duct work under the dash. The type 2 air package in our 77 eleganza would frost your knees.
JR Wright
78 Buskirk Stretch
75 avion still undergoing reconstruction.
> On Jun 24, 2018, at 8:15 PM, John Shutzbaugh wrote:
>
> Even though it is a late model coach, I could use MORE air. The temp is ok, just not enough of it.
>
> John
>
> --
> John Shutzbaugh, Vacaville, CA, ncserv@aol.com;
> 77 Eleganza, bought it new, can't blame PO, and
> 78 Buskirk stretch, "What were we thinking?"
>
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| Re: the HVAC designs of Mark Wall [message #333961 is a reply to message #333935] |
Sun, 24 June 2018 23:49 |
KB
Messages: 1262
Registered: September 2009
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JohnS wrote on Sun, 24 June 2018 09:27Karen, I was watching for the results of the modification you were doing with the blower mounted in the cockpit, but must have missed the outcome. Was noise the main result? Did it cool better? It's pretty hot in my 78 & I too am looking to change things.
John
Hey John,
I built the floor box, hooked up the blower and wired it up enough to test, but decided against going any further.
Since we have the max air version, I'd have had to remove the max air door or it would only have been
blowing on the blower. Since that's a lot more work, I decided to think about it some more.
The combination of noise and the difficulty of incorporating fresh air was what made me decide against it.
It's a nice blower though, so kind of a shame I can't use it.
Karen
1975 26'
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| Re: [GMCnet] the HVAC designs of Mark Wall [message #333962 is a reply to message #333947] |
Sun, 24 June 2018 23:57 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
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Make sure the hot water is not flowing through the heater core and the door
is shut.
It is amasing what those things contribut to low cooling.
On Sun, Jun 24, 2018 at 5:15 PM, John Shutzbaugh
wrote:
> Even though it is a late model coach, I could use MORE air. The temp is
> ok, just not enough of it.
>
> John
>
> --
> John Shutzbaugh, Vacaville, CA, ncserv@aol.com;
> 77 Eleganza, bought it new, can't blame PO, and
> 78 Buskirk stretch, "What were we thinking?"
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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| Re: the HVAC designs of Mark Wall [message #334040 is a reply to message #333850] |
Tue, 26 June 2018 12:13 |
Bill Van Vlack
Messages: 419
Registered: September 2015
Location: Guemes Island, Washington
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Quote:
Since we have the max air version, I'd have had to remove the max air door or it would only have been
blowing on the blower.
"Blowing on the blower"... Isn't the max air door chamber above and separated from the evap coil chamber?
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.
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| Re: the HVAC designs of Mark Wall [message #334108 is a reply to message #333850] |
Wed, 27 June 2018 16:13 |
Bill Van Vlack
Messages: 419
Registered: September 2015
Location: Guemes Island, Washington
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I see what you mean... I did some sketchup drawings that show ducts added to the fan inlets to prevent that short-circuiting.
I envisioned them routing up under the dash, and covering the exposed parts with a little cabinet, but for a lot of reasons, I agree that this seems like the wrong way to go. The fan on the front of the HVAC box seems like it provides the shortest air paths, at least forward of the firewall.
I think any solution needs to allow modulating between 100% recirc and 100% outside air for max cooling and defrost/defog. The Type II unit would need an additional damper for that. For defog, the AC and heat have to run at the same time, which I think means a control change as well.
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.
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| Re: the HVAC designs of Mark Wall [message #334116 is a reply to message #334108] |
Wed, 27 June 2018 19:26 |
KB
Messages: 1262
Registered: September 2009
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I upgraded my drawings to try and show the air paths better, color coded.
Red is warm air, yellow is air in the blower/pressure chamber, blue is cool air.
http://www.gmcmhphotos.com/photos/hvac-original-and-mods/p64915-airflow-all.html
Ironically, it's a lot easier to go from a 73/74 box to the later design than from the 75/76 version.
The 73 already has the recirc door and you don't have to remove the max-air slot. They used the recirc door
vacuum pot to power the max air door, and didn't cut a hole for recirc in the 75/76.
You can see why: they were trying to separate the max air output from the blower inlet air.
Once they added the type-II external duct under the dash, that's no longer a problem.
I tried to find a unit from a modern vehicle, but it's all so convoluted and tied to the exact shape of each vehicle that
it's not really feasible to fit in our available space.
I also thought a lot about doing Mark Wall's later iteration, but decided there was no real advantage in terms of space efficiency.
The problems are the same, and there's a lot more vertical than horizontal space available outside the firewall.
Plus, we already have the box. So, basically, I'm just re-creating the 77/78 design in a 75 coach, with a little variation
from how Mark did it. This version has both recirc and outside air, and the defroster door should work as designed.
It really requires you to remove the box from the coach, but I found that you can (very gently) remove the evaporator core
with the hoses still attached and tie it out of the way. It's easy to disconnect the heater core, and (with someone
stationed to protect the evaporator) you can slide the box down and out through the grill opening.
Karen
1975 26'
[Updated on: Wed, 27 June 2018 19:28] Report message to a moderator |
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| Re: the HVAC designs of Mark Wall [message #334117 is a reply to message #333850] |
Wed, 27 June 2018 20:06 |
Bill Van Vlack
Messages: 419
Registered: September 2015
Location: Guemes Island, Washington
Karma: 14
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From the diagrams, it looks like the major difference btw 74-74 and 77-78 is mostly the new duct plus the openings in the firewall and box to make the connection. Certainly see how the '76 is 'boxed' into a corner in all of this. I think if I could provide some recirc to the blower inlet, the rest I could live with.
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.
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