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| [GMCnet] Dash Air Conditioning [message #143095] |
Mon, 12 September 2011 13:21  |
Dolph Santorine
Messages: 1236
Registered: April 2011
Location: Wheeling, WV
Karma: -41
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These questions are coming out off a brief conversation I had with Ken Henderson about the dash A/C, and some of the work that he's been doing with his unit.
He mentioned the A6 Compressor ranges from 27,000 BTU to 42,000 BTU (4,000 RPM). (as designed, running R12)
The rooftop A/C units that most coaches have at least one of are generally 13,500 to 15,000 BTU (Limited to 15,000 because of electrical considerations).
If we use midpoints on both (the rooftops assuming 27,000 BTU) and the dash unit at 34,500 BTU, I don't understand why the coach would not have a unified system that did both.
I know that intercity busses generally have a unified system, but they are huge (8 tons and up), and designed to have many 500 BTU/hr. humans crammed into fairly small spaces.
I guess I'm not understanding why the dash unit should not be more than sufficient to cool the entire coach.
Thoughts? Observations?
Dolph
DE N8JPC
Wheeling, West Virginia
dolph@dolphsantorine.com
1977 GMC 26' Palm Beach
TZE167V100820
1976 GMC 26' Donor Coach
TZE166V101610
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| Re: [GMCnet] Dash Air Conditioning [message #143096 is a reply to message #143095] |
Mon, 12 September 2011 13:30  |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
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Dolph,
That's all true and the dash AC has loads of capacity, but it's asthmatic. As I understand it the compressor, condensor, and evaporator are plenty big enough, there just is not enough airflow over the evaporator to do any good. Others who have added a second evaporator have reported great things. Something like "spitting ice cubes", "freezing beef" and so on with the extra condensor attached to the existing system.
I know that Jim K sells an add-on unit that some have put in the traditional dash area, others under the passenger seat, and one fellow took a condensor from a GMC Van and mounted it at the rear of the coach. (I don't know how that one worked out, but it sure looked promissing!)
If you no longer have an r12 charge, pull a vacuum and shoot in some Duracool.Â
Here is a link to Jim K's site http://appliedgmc.com/level.itml/icOid/944
Larry Davick
Fremont, California
The Mystery Machine
'76 (ish) Palm Beach
Larry Davick
Fremont, California
The Mystery Machine
'76 (ish) Palm Beach
----- Original Message -----
From: "Dolph Santorine" <dolph@dolphsantorine.com>
To: gmclist@temp.gmcnet.org
Sent: Monday, September 12, 2011 11:21:37 AM
Subject: [GMCnet] Dash Air Conditioning
These questions are coming out off a brief conversation I had with Ken Henderson about the dash A/C, and some of the work that he's been doing with his unit.
He mentioned the A6 Compressor ranges from 27,000 BTU to 42,000 BTU (4,000 RPM). (as designed, running R12)
The rooftop A/C units that most coaches have at least one of are generally 13,500 to 15,000 BTU (Limited to 15,000 because of electrical considerations).
If we use midpoints on both (the rooftops assuming 27,000 BTU) and the dash unit at 34,500 BTU, I don't understand why the coach would not have a unified system that did both.
I know that intercity busses generally have a unified system, but they are huge (8 tons and up), and designed to have many 500 BTU/hr. humans crammed into fairly small spaces.
I guess I'm not understanding why the dash unit should not be more than sufficient to cool the entire coach.
Thoughts? Observations?
Dolph
DE N8JPC
Wheeling, West Virginia
dolph@dolphsantorine.com
1977 GMC 26' Palm Beach
TZE167V100820
1976 GMC 26' Donor Coach
TZE166V101610
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: [GMCnet] Dash Air Conditioning [message #143102 is a reply to message #143095] |
Mon, 12 September 2011 14:51 |
idrob
Messages: 645
Registered: January 2005
Location: Central Idaho
Karma: 0
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| Dolph Santorine wrote on Mon, 12 September 2011 11:21 |
I guess I'm not understanding why the dash unit should not be more than sufficient to cool the entire coach.
Thoughts? Observations?
Dolph
DE N8JPC
|
Although GM had the Harrison division available to design the dash AC unit, apparently either Harrison gave it to a freshman designer or it was some kind of a rush job. In general GM AC units in cars of that era were excellent. The one in the GMC was not. At any rate, the dash air leaves a lot to be desired.
Some feel it is air flow through the system that is the only problem, and have worked on improving that aspect. I am sure it is part of the issue. However, having had mine apart when I owned my rig, it is my contention that the evaporator is simply too small for the job. Although the engine compressor has a lot of capacity, it cannot be utilized by the undersized, multi row, deep and narrow evaporator. You can only absorb so much heat in a given evaporator area, and I feel the original is just too small. Remember, this is my opinion.
Those who have added second evaporators have had very good results. By doing that both the evaporator area is increased substantially and the airflow is much more direct. The original compressor has the capacity for two evaporators.
GMC simply blew it when it came to the dash air in the coach. Later ones (77 and 78) were much better, but still are a bit marginal from what I understand.
Rob Allen
former owner of '76 x-PB
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| Re: [GMCnet] Dash Air Conditioning [message #143108 is a reply to message #143095] |
Mon, 12 September 2011 16:10 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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Senior Member |
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| Dolph Santorine wrote on Mon, 12 September 2011 13:21 |
..He mentioned the A6 Compressor ranges from 27,000 BTU to 42,000 BTU (4,000 RPM). (as designed, running R12)
The rooftop A/C units that most coaches have at least one of are generally 13,500 to 15,000 BTU (Limited to 15,000 because of electrical considerations).
If we use midpoints on both (the rooftops assuming 27,000 BTU) and the dash unit at 34,500 BTU, I don't understand why the coach would not have a unified system that did both.
I know that intercity busses generally have a unified system, but they are huge (8 tons and up), and designed to have many 500 BTU/hr. humans crammed into fairly small spaces.
I guess I'm not understanding why the dash unit should not be more than sufficient to cool the entire coach.
Thoughts? Observations?
Dolph
DE N8JPC
Wheeling, West Virginia
dolph@dolphsantorine.com
1977 GMC 26' Palm Beach
TZE167V100820
1976 GMC 26' Donor Coach
TZE166V101610
|
I have toyed with the idea of removing the roof A/C at the front and substituting one of the "auxilliary" evaporator units teed off the A6 compressor on the engine.
This sounds like your idea of the unified system like municipal busses have.
I would leave the 120VAC roof unit in the rear to cool the living area when tied to "shore" power or running off generator.
Of course I will have to get dash A/C installed, since mine came from the factory without dash A/C and none of the POs corrected that deficiency. At least I am starting with a clean slate and I can install dash air from one of the newer models with a system that actually worked.
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| Re: [GMCnet] Dash Air Conditioning [message #143119 is a reply to message #143095] |
Mon, 12 September 2011 17:08 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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G'day,
What would be the power source to drive the compressor when parked?
Regards,
Rob M.
Sydney, Australia
-----Original Message-----
From: Dolph Santorine
These questions are coming out off a brief conversation I had with Ken Henderson about the dash A/C, and some of the work that he's
been doing with his unit.
He mentioned the A6 Compressor ranges from 27,000 BTU to 42,000 BTU (4,000 RPM). (as designed, running R12)
The rooftop A/C units that most coaches have at least one of are generally 13,500 to 15,000 BTU (Limited to 15,000 because of
electrical considerations).
If we use midpoints on both (the rooftops assuming 27,000 BTU) and the dash unit at 34,500 BTU, I don't understand why the coach
would not have a unified system that did both.
I know that intercity busses generally have a unified system, but they are huge (8 tons and up), and designed to have many 500
BTU/hr. humans crammed into fairly small spaces.
I guess I'm not understanding why the dash unit should not be more than sufficient to cool the entire coach.
Thoughts? Observations?
Dolph
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Dash Air Conditioning [message #143126 is a reply to message #143102] |
Mon, 12 September 2011 17:24 |
ejuk8em
Messages: 90
Registered: July 2010
Karma: 0
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Member |
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I can't speak for the newer models, but in our '73 - the dash AC is like a fine old wine with a complex flavor.... (i.e. On maximum it has just a "hint" of cooling!!!! )
I've check the charge numbers and feel pretty confident we are close using DuraCool. Like Rob I think the answer lies in an undersized evaporator. The tricky part in thinking to correct this is where to install either a second evaporator, or one that is more appropriately sized, and keep it out of the way of the engine compartment door.
FYI to the group. Still holding on to "The Stay Dog".... even though we have an SOB to use for this summer. The wife wants the GMC gone... but I'm really, really, really dragging my feet. I'm thinking that we can sell the SOB once we get the GMC put back together. After 30 plus years of marriage one would think we would be a bit more on the same page. ;-) I'm not sure if I should ask for prayers for the GMC or for me.
Have fun in Goshen!!! Wish we could have joined in. My brother passed just before the event and we just didn't feel good about being gone.
Take care and safe travels,
Lyle
Lyle A. Rigdon, Retired Superintendent
'73 Pineapple Yellow Sequoia
"The Stray Dog"
Pawnee, IL 62558
Pawnee Pride - Live It!
--- On Mon, 9/12/11, Rob Allen <profmail@wildblue.net> wrote:
From: Rob Allen <profmail@wildblue.net>
Subject: Re: [GMCnet] Dash Air Conditioning
To: gmclist@temp.gmcnet.org
Date: Monday, September 12, 2011, 2:51 PM
Dolph Santorine wrote on Mon, 12 September 2011 11:21
> I guess I'm not understanding why the dash unit should not be more than sufficient to cool the entire coach.
>
> Thoughts? Observations?
>
> Dolph
>
> DE N8JPC
Although GM had the Harrison division available to design the dash AC unit, apparently either Harrison gave it to a freshman designer or it was some kind of a rush job. In general GM AC units in cars of that era were excellent. The one in the GMC was not. At any rate, the dash air leaves a lot to be desired.
Some feel it is air flow through the system that is the only problem, and have worked on improving that aspect. I am sure it is part of the issue. However, having had mine apart when I owned my rig, it is my contention that the evaporator is simply too small for the job. Although the engine compressor has a lot of capacity, it cannot be utilized by the undersized, multi row, deep and narrow evaporator. You can only absorb so much heat in a given evaporator area, and I feel the original is just too small. Remember, this is my opinion.
Those who have added second evaporators have had very good results. By doing that both the evaporator area is increased substantially and the airflow is much more direct. The original compressor has the capacity for two evaporators.
GMC simply blew it when it came to the dash air in the coach. Later ones (77 and 78) were much better, but still are a bit marginal from what I understand.
--
Rob Allen
former owner of '76 x-PB
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| Re: [GMCnet] Dash Air Conditioning [message #143150 is a reply to message #143119] |
Mon, 12 September 2011 20:21 |
Dolph Santorine
Messages: 1236
Registered: April 2011
Location: Wheeling, WV
Karma: -41
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Rob:
I was toying with an electric motor.... and I was not thinking of having it driven off the engine at all, but from a water cooled generator engine. Seems to be a lot of the Honda engines around less the windings that generate electricity.
But there are some things that are not adding up, and I need look at the basic assumptions:
What I know:
Most 6kw generators use 10 ish horsepower engines (check for reasonability at .746 kw per hp)
The Dometic 15,000 BTU rooftop unit's compressor requires 12.9 amps at 115vac Their literature claims you can run two of these on a 5kw generator.
12.9 amps at mains is 1.5 kw
I think I've been been using 5hp per ton of A/C for a long time and it's flat out wrong.
So, it looks to take a lot less shaft horsepower than I expected (a good thing).
This is most likely nothing more than a design exercise and an interesting train of thought.
Our local emergency management folks recently purchased a SOB tricked out with about $200K of communications gear. You know, in case the Taliban decides to target dying steel towns.
It has a very trick air conditioner that is allegedly based on what they use for Greyhound Dog transport. Cold air return is a fan sized opening (two on their coach). Blower air comes out of maybe 2" outlets up and down the roof of the coach. The entire package on the roof is maybe 6" high (and provides a platform for antenna's and such). I'm going to get to look at more of it week after next, but I was told it runs off the coach engine or mains.
Which leads me to ask, Rob... since you handled the RH drive issue, what did you do for mains on the Aus coach?
Dolph
DE N8JPC
Wheeling, West Virginia
dolph@dolphsantorine.com
1977 GMC 26' Palm Beach
TZE167V100820
1976 GMC 26' Donor Coach
TZE166V101610
On Sep 12, 2011, at 6:08 PM, Rob Mueller wrote:
> G'day,
>
> What would be the power source to drive the compressor when parked?
>
> Regards,
> Rob M.
> Sydney, Australia
>
> -----Original Message-----
> From: Dolph Santorine
>
> These questions are coming out off a brief conversation I had with Ken Henderson about the dash A/C, and some of the work that he's
> been doing with his unit.
>
> He mentioned the A6 Compressor ranges from 27,000 BTU to 42,000 BTU (4,000 RPM). (as designed, running R12)
>
> The rooftop A/C units that most coaches have at least one of are generally 13,500 to 15,000 BTU (Limited to 15,000 because of
> electrical considerations).
>
> If we use midpoints on both (the rooftops assuming 27,000 BTU) and the dash unit at 34,500 BTU, I don't understand why the coach
> would not have a unified system that did both.
>
> I know that intercity busses generally have a unified system, but they are huge (8 tons and up), and designed to have many 500
> BTU/hr. humans crammed into fairly small spaces.
>
> I guess I'm not understanding why the dash unit should not be more than sufficient to cool the entire coach.
>
> Thoughts? Observations?
>
> Dolph
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Dash Air Conditioning [message #143156 is a reply to message #143126] |
Mon, 12 September 2011 20:49 |
Guy Lopes
Messages: 499
Registered: April 2004
Location: Sacramento, CA
Karma: 3
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Senior Member |
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Lyle,
I'm sorry to hear about your Brother's passing. My condolences to you and
your family.
Guy in Sacramento
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Lyle A. Rigdon
Sent: Monday, September 12, 2011 3:25 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Dash Air Conditioning
<snip>
bit more on the same page. ;-) I'm not sure if I should ask for prayers
for the GMC or for me.
Have fun in Goshen!!! Wish we could have joined in. My brother passed just
before the event and we just didn't feel good about being gone.
Take care and safe travels,
Lyle
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Guy Lopes
76 Birchaven "Orion"
Sacramento, CA
W6TOL
www.GMC-Guy.com
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| Re: [GMCnet] Dash Air Conditioning [message #143160 is a reply to message #143150] |
Mon, 12 September 2011 21:15 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Dolph,
John Sharpe has a Winnebago Spectrum RV that has two electrical driven compressors that supply A/C down the length of the ceiling. I
think it has a separate engine powered dash air system.
JimB has a Airstream Motorhome that was outfitted as a hearse. IIRC it had an engine powered compressor that provided ceiling roof
air. He installed a Penguin to replace that system as it didn't work.
Funny you should ask about the house power conversion on my GMC here, Mark Bennett and I were talking about it yesterday. He advised
that in Australia motorhomes MUST have stranded wire. The reason being is the walls move and solid wire could break and short out
against the metal in the walls.
However, The Blue Streak's PO converted it to 240vac 50hz by removing the Onan and installing a Chinese generator. He swapped out
the US power points for Aussie power points. Anything that ran on 120VAC got replaced with a unit that ran on 240VAC. Funny thing is
he left the old buzz box and hooked up a step down transformer to it. The buzz box will get replaced.
BTW I've sent you an off net message with a couple of files of off frame restos.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: Dolph Santorine
Rob:
I was toying with an electric motor.... and I was not thinking of having it driven off the engine at all, but from a water cooled
generator engine. Seems to be a lot of the Honda engines around less the windings that generate electricity.
But there are some things that are not adding up, and I need look at the basic assumptions:
What I know:
Most 6kw generators use 10 ish horsepower engines (check for reasonability at .746 kw per hp)
The Dometic 15,000 BTU rooftop unit's compressor requires 12.9 amps at 115vac Their literature claims you can run two of these on a
5kw generator.
12.9 amps at mains is 1.5 kw
I think I've been been using 5hp per ton of A/C for a long time and it's flat out wrong.
So, it looks to take a lot less shaft horsepower than I expected (a good thing).
This is most likely nothing more than a design exercise and an interesting train of thought.
Our local emergency management folks recently purchased a SOB tricked out with about $200K of communications gear. You know, in case
the Taliban decides to target dying steel towns.
It has a very trick air conditioner that is allegedly based on what they use for Greyhound Dog transport. Cold air return is a fan
sized opening (two on their coach). Blower air comes out of maybe 2" outlets up and down the roof of the coach. The entire package
on the roof is maybe 6" high (and provides a platform for antenna's and such). I'm going to get to look at more of it week after
next, but I was told it runs off the coach engine or mains.
Which leads me to ask, Rob... since you handled the RH drive issue, what did you do for mains on the Aus coach?
Dolph
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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