Engine driven roof top AC to replace Dash AC

G

george butts

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Feb 29, 2012
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Has anyone installed a roof AC unit similar to those used on a bus or similar to Airport shuttle van. We all know the dash AC does only a marginal
job to cool the front and forget the entire coach.
--
George Butts
Las Vegas Nevada
73 "Custom 26' Q" & 76 23' Birchaven
71 Honda 600 Coupe & 01 Tracker Toads
 
Interesting thought.
I don’t specifically remember that having been done on a GMC.
It would remove the condenser air flow restriction and heat from
the radiator for improved cooling and less problems with vapor lock.
It may be a third AC on the roof?
Definitely could cool the bridge.
Lots of pros and cons.

Marsh (who rarely post anymore) Wilkes


-----Original Message-----
From: GEORGE BUTTS via Gmclist
Sent: Sunday, July 30, 2017 2:32 PM
To: gmclist
Cc: GEORGE BUTTS
Subject: [GMCnet] Engine driven roof top AC to replace Dash AC

Has anyone installed a roof AC unit similar to those used on a bus or
similar to Airport shuttle van. We all know the dash AC does only a
marginal
job to cool the front and forget the entire coach.
--
George Butts
Las Vegas Nevada
73 "Custom 26' Q" & 76 23' Birchaven
71 Honda 600 Coupe & 01 Tracker Toads

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Might just be easier to run with the genset running and turning on the roof air. Works in my coach. One of the auxiliary coolers would be also to deal
with than a roof mount. Look cleaner also.
Tom, MS II1975 Avion 4 sale
--
1975 GMC Avion
KA4CSG
 
George Butts Wrote: We all know the dash AC does only a marginal job to
cool the front and forget the entire coach.

George "I believe you" when you made the comment that dash AC is
marginal. However, the cooling system is plenty "large enough" (capacity)
to handle "most" of our demands properly maintained. I do not believe
hanging more hardware on your coach is the answer.

The real issue is the HVAC (Heating, Ventilation, Air Conditioning) box AIR
FLOW . The Harrison Division of GM designed the system with no apparent
thought to air flow velocity .......OR..........the GM Truck & Bus guys
said "give me something that will fit into this space"! So we got a system
that only pressurizes the HVAC box and ignores air velocity and direction.
Most of us are aware that the blower on a traditional furnace located in
the basement of a home has a centrifugal fan that pushes air up
through the heating and AC coils to the registers on the 1st and 2nd
floors. That is what is most efficient. It is a Laminar Air flow model
with little Air Flow turbulence. Many Owners think that we have this
model for dash AC in our Coaches.

That is untrue.

Just think if, 1) a centrifugal blower fan in our home basement was
turned upside down and pushed air toward the basement floor 1st
..............and 2) was then was ducted to the right or left into the
chamber that housed the heating and AC coils! THAT CREATES TWO TURBULENT
AIR FLOW EVENTS! That is exactly the strategy our coaches have
employed..........no matter what year it was built and what attempts by GM
employed to rescue the design.

I have only minor exposure to "marginal AC" when traveling 5000 miles to
the Rally in South Dakota from Florida in my 23B. Yea it Sucks! I
recently posted on the GM Photo site a Modification that DOES NOT require a
complete revision of the HVAC Box or any of the controls. It is a one day
project for some, most will say a week end. It requires one Purchased
part ........a double centrifugal fan assembly and the construction of a
small duct from the floor of the coach to the HVAC box. If the
Centrifugal fan is used from my posting, removing wires from the existing
HI, Med, and Lo resistors on the driver side of the HVAC box and extending
them to the new Centrifugal Double fan is a trivial task. We now can look
forward to Laminar, not Turbulent air flow

SEE:
http://www.gmcmhphotos.com/photos/i-need-more-air/p63443-a-hvac-blower-modification.html

HOW CAN I HELP?
--
Regards,

Tom Pryor
4188 Limerick Dr
Lake Wales, Fl 33859
Cell 248 470 9186

Living on a waterfront is not a matter of life or death. Its more
important than that.
 
Bob Heller also says it's an airflow problem. His solution was to add ports & 2" flex ducts to the existing box and vent them into the cabin
floorboard.
--
77 Royale Coachmen Side Dry Bath
76 Birchaven Coachmen Side Wet Bath
76 Eleganza
Elizabeth City, NC
 
Thanks Tom, great write up and project. Not sure that I followed the complete concept though. For clarification, are you are using the existing
ducts in the dash but doing away with the existing blower motor and fan. If so I have a 1973 which has different dash ducts from the one in the
pictures. I assume your modification with work just as well for a 73? Also I assume it gives the same benefits for the heater and defrost.
--
George Butts
Las Vegas Nevada
73 "Custom 26' Q" & 76 23' Birchaven
71 Honda 600 Coupe & 01 Tracker Toads
 
Are you saying you are getting close to the same amount of cooling from the
engine hardware as you would get from a roof unit running off the Onan
generator?

On Sun, Jul 30, 2017 at 8:03 PM, GEORGE BUTTS via Gmclist <

> Thanks Tom, great write up and project. Not sure that I followed the
> complete concept though. For clarification, are you are using the existing
> ducts in the dash but doing away with the existing blower motor and fan.
> If so I have a 1973 which has different dash ducts from the one in the
> pictures. I assume your modification with work just as well for a 73?
> Also I assume it gives the same benefits for the heater and defrost.
> --
> George Butts
> Las Vegas Nevada
> 73 "Custom 26' Q" & 76 23' Birchaven
> 71 Honda 600 Coupe & 01 Tracker Toads
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--

*John Phillips*
 
Thomas,

> If the Centrifugal fan is used from my posting, removing wires from > the existing HI, Med, and Lo resistors on the driver side of the >
HVAC box and extending them to the new Centrifugal Double fan is a >
trivial task. We now can look forward to Laminar, not Turbulent air > flow
is the end result, that you no longer utilize the existing HVAC at all,
ie. direction of air flow for heating and/or windshield de-fogging, or
is this purely for making sure the A/C is providing the needed cooling
to the poor sweating cockpit inhabitants?
--

Best regards

Peer Oliver Schmidt
PGP Key ID: 0x83E1C2EA

'76a Eleganza II, CA
'73 Sequoia, VA
 
Is this mostly better air flow (as in vent) rather than real refrigeration
cooling?

On Sun, Jul 30, 2017 at 8:25 PM, Peer Oliver Schmidt GMC <

> Thomas,
>
> > If the Centrifugal fan is used from my posting, removing wires from >
> the existing HI, Med, and Lo resistors on the driver side of the >
> HVAC box and extending them to the new Centrifugal Double fan is a >
> trivial task. We now can look forward to Laminar, not Turbulent air > flow
> is the end result, that you no longer utilize the existing HVAC at all,
> ie. direction of air flow for heating and/or windshield de-fogging, or
> is this purely for making sure the A/C is providing the needed cooling
> to the poor sweating cockpit inhabitants?
> --
>
> Best regards
>
> Peer Oliver Schmidt
> PGP Key ID: 0x83E1C2EA
>
> '76a Eleganza II, CA
> '73 Sequoia, VA
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--

*John Phillips*
 
SO OKAY,

GEORGE B. The duct work changes made by GM on early coaches were mostly
to redirect what little air came out of the HVAC box and where the air came
from, inside or outside. This modification that I am employing does not
affect air management when it leaves the HVAC box..............the attempt
is to create more directional air velocity and laminar flow as air moves
through the HVAC box into what ever ventilating system you have. Yes it
does do away with the existing motor and centrifugal fan and all the HVAC
box inlets are abandoned. You will always use 100% recirculating air.
Some the GM modifications used only outside air and no recirculation
choice.

As I thought more about this change, it occurred to me that we could
use the original OEM motor/fan housing and refit it to the floor with a
single duct to the bottom of the HVAC Box. No new parts and just add wire
to reach the new location of the Motor and Fan, EH?

Peer Oliver Schmidt,

Yes we keep existing HVAC box, all the ventilation ducting and vacuum
actuators, as well as controls in the dash. Closing all under hood inlet
air openings from the old arrangement now eliminates heat created by the
engine and radiator to be ingested into the box. The only downside to this
modification is that you will no longer have access to outside air. When
you select "Vent" only on your dash, you won't get anything because that
feature is blocked off.

is the end result, that you no longer utilize the existing HVAC at all,
ie. direction of air flow for heating and/or windshield de-fogging, or
is this purely for making sure the A/C is providing the needed cooling
to the poor sweating cockpit inhabitants?
--
Regards,

Tom Pryor
4188 Limerick Dr
Lake Wales, Fl 33859
Cell 248 470 9186

Living on a waterfront is not a matter of life or death. Its more
important than that.
 
tom,

any pictures of the completed floor unit? Is there a reason you were not able to just blow directly into the re-circulation duct at the bottom of
the dash? I am just curious how much space this takes up, as my 75, there is limited space in that area to allow the engine lid to open up.

I was thinking the other day, about what it would take to add a sucker fan at the center dash outlets of my 75, when i seen your post on this.
--
Jon Roche
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/
 
This is on my list of 'sometime' mods, which I will probably address next time I get roasted on a summer trip.

Additionally, although this will solve the driver/front passenger cooling concern, I'm investigating some sort of air handler for the rest of the
coach. According to an article in Hemmings, the A-6 compressor is capable of 27,000 BTU at 2000 RPM, improving to over 40,000 at 4K. This at 240PSI
outlet pressure. Easily enough to keep the interior of the coach cool when traveling. I'm thinking a roof mounted condenser a la flatfront Econoline
vans from the 60s and a couple of evaporator/fan units strategically placed, and some plumbing.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
> tom,
>
> any pictures of the completed floor unit? Is there a reason you were not able to just blow directly into the re-circulation duct at the bottom
> of the dash? I am just curious how much space this takes up, as my 75, there is limited space in that area to allow the engine lid to open up.
>
> I was thinking the other day, about what it would take to add a sucker fan at the center dash outlets of my 75, when i seen your post on this.

OK- I finally got to look at Tom's pictures closely and not on my phone. I see he does not have the re-circulation duct that I can tell in his
pictures, that I have on my 75. On my 75 there is like a 2" tall x 14" long opening into the HVAC system right center bottom of dash that is the air
source for the re-circulation(from what I remember and can tell). I am going to look a little closer and do some experimenting on my ducts. The
final answer is to add an aux evaporator, but possibly adding this sort of fan to really force air through the existing system may work well, and be
something very quick, easy and inexpensive to do.

--
Jon Roche
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/
 
Used to have a flower shop, and the dash air in the vans was inadequate for
floral delivery. E-150 fords. Solved this by tapping into the dash air
compressor and running refrigerant lines to the rear of the van to a
vintage air a/c unit suspended from the van roof inside the cargo area. It
would freeze your butt off on the hottest days. The flowers loved it, too.
I wouldn't be too keen on anything that interfered with access to the
engine hatch on a GMC. Too much vital stuff under there that needs to be
looked at on a regular basis. Maintenence on a coach is not a seldom
activity. I work on coaches that I know have not been looked at under the
hatch in months because of all the crap piled up on the hatch.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Jul 31, 2017 9:51 AM, "Johnny Bridges via Gmclist" <

This is on my list of 'sometime' mods, which I will probably address next
time I get roasted on a summer trip.

Additionally, although this will solve the driver/front passenger cooling
concern, I'm investigating some sort of air handler for the rest of the
coach. According to an article in Hemmings, the A-6 compressor is capable
of 27,000 BTU at 2000 RPM, improving to over 40,000 at 4K. This at 240PSI
outlet pressure. Easily enough to keep the interior of the coach cool when
traveling. I'm thinking a roof mounted condenser a la flatfront Econoline
vans from the 60s and a couple of evaporator/fan units strategically
placed, and some plumbing.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me
in hell" - ol Andy, paraphrased

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The two auxiliary evaporators I installed are published at 17k btu, so double is 34k, plus the original Harrison, I'm running frosty cool and still
froze one of the evaporators. Although I had planned on installing a parallel flow condenser to compensate for additional load, it was a little to
big and didn't fit between frame rails. So I know the serpentine condenser is still up to the task. My last trip to Massachusetts in 90 degree
weather was comfortable. I did add clear shower curtains, which I may need to get to Dillard,GA in a couple weeks. Seems traveling south, the sun
beating in the windshield is difficult to avoid, and may overpower my triple evaporators.
--
Sean and Stephanie
73 Ex-CanyonLands 26' #317 "Oliver"
Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1 LSD Honda 6500 inverter gen.

Colonial Travelers
 
I put an Aux unit under the couch on the drivers side. I have a fan switch under the drivers seat.

It has two outlets, one points back, the other at the dinette. it really cools the coach down.

But the dash air could be beefed up

________________________________
From: Gmclist on behalf of Thomas Phipps
Sent: Sunday, July 30, 2017 5:06:02 PM
To: gmclist
Subject: Re: [GMCnet] Engine driven roof top AC to replace Dash AC

Might just be easier to run with the genset running and turning on the roof air. Works in my coach. One of the auxiliary coolers would be also to deal
with than a roof mount. Look cleaner also.
Tom, MS II1975 Avion 4 sale
--
1975 GMC Avion
KA4CSG

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Unsubscribe or Change List Options:
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You probably have a bigger problem with humidity than you have with
temperature. That would account for the icing. We in the west have high
temperature and low humidity. Icing is usually not a problem out here. Cure
for high humidity is greater airflow across the coils along with greater
cooling capacity. Glad I don't live in that part of the country. Supposed
to be near 100 degrees here today, 105 later in the week. When it gets over
90 in the shop, it is downright uncomfortable.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> The two auxiliary evaporators I installed are published at 17k btu, so
> double is 34k, plus the original Harrison, I'm running frosty cool and still
> froze one of the evaporators. Although I had planned on installing a
> parallel flow condenser to compensate for additional load, it was a little
> to
> big and didn't fit between frame rails. So I know the serpentine
> condenser is still up to the task. My last trip to Massachusetts in 90
> degree
> weather was comfortable. I did add clear shower curtains, which I may
> need to get to Dillard,GA in a couple weeks. Seems traveling south, the sun
> beating in the windshield is difficult to avoid, and may overpower my
> triple evaporators.
> --
> Sean and Stephanie
> 73 Ex-CanyonLands 26' #317 "Oliver"
> Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1 LSD
> Honda 6500 inverter gen.
>
> Colonial Travelers
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
JimH, What you described is what JimB did to the dash air on my '73 x-CL. Tee'd
in an under dash vintage air type unit to my existing dash a/c 14 years ago and like you
said "will freeze your butt off". Only problem I've had in all this time is I've had to
add one can of R-12.

Works for me here in Florida.

jim Galbavy
'73 x-CL (ANNIE)
Lake Mary, FL
 
As Johnny Bridges stated the output of our A6 Compressor is an impressive
26000 BTU at 2000 RPM. We are just not able to distribute it efficiently
and effectively, just say'n. I have a new vintage air unit that I can
place under living area furniture if required. Don't plan to plumb it in.

Some have said that the modification will block the engine hatch
access...........no it won't. See: http://www.gmcmhphotos
.com/photos/i-need-more-air/p63452-f-img-09691.html

Also some comments that the return air duct is not shown in my images.
Again looking at the same image the firewall recirculating opening is shown
but not blocked off yet. That will be completed when I reinstall the IP.
http://www.gmcmhphotos.com/photos/i-need-more-air/p63452-f-img-09691.html

ALSO, IMHO ducting air thru the recirculating vent will only create more
turbulent air flow and not solve the air management problem.......The air
flow must come from lower quadrant and behind the HVAC
Box.......................KISS! knuff said.

Regards,

Tom Pryor
4188 Limerick Dr
Lake Wales, Fl 33859
Cell 248 470 9186

Living on a waterfront is not a matter of life or death. Its more
important than that.
 
2 Comments:

Keep in mind, the A6 output quotes are at compressor rpm, not necessarily engine rpm. Not sure if the compressor is underdriven or overdriven, but I
believe it is overdriven.

As for the heat through the windshield, they have these new (well, newish) window tints out that are mostly clear and can be installed on a
windshield, but block a good percentage of the heat and infrared energy.

No comment on the legality of these tints, but I was considering the 90 or maybe 70 tint below on my GMC's windshield:

http://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Automotive-Window-Film-Crystalline-Series?N=5002385+3292716668&rt=rud

From what I understand, they are clear enough not to attract any attention from John Q. Law, and not impede in any significant way, your night
vision....
--
Mark S. '73 Painted Desert,
Manny 1 Ton Front End,
Howell Injection,
Leigh Harrison 4bag and Rear Brakes,
Fort Worth, TX
 
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