[GMCnet] WE ALL NEED MORE AIR

[Thomas Pryor]

Hi Folks. I just completed a modification to my HVAC box that can easily
copied by any and all.

It is generally known that the air flow in our OEM HVAC boxes are anemic at
best. The "why" in my opinion is the side mounted squirrel cage fan expels
air that must change directions twice before getting to cooling or heating
fins. It is generally agreed that the capacity of our A/C compressor and
system is sufficient. After reviewing the efforts of Ken Henderson and
others I wondered if there might be a way to modify the system without
removing the whole HVAC box to improve air flow and efficiency.

This modification is JWID:

1. It requires cutting an access hole in the floor of the coach to get
access to the Lower portion of the HVAC box, then cutting two square
holes in the box.

http://www.gmcmhphotos.com/
photos/i-need-more-air/p63444-thumb-img-0955-1024.html

2. I then Fashioned a Plenum to connect the floor to box.
http://www.gmcmhphotos.com/
photos/i-need-more-air/p63448-plenum-sketch.html
http://www.gmcmhphotos.com/
photos/i-need-more-air/p63449-thumb-img-0957-10241.html

3. A new floor insert was made and installed to accommodate a MCC
fan blower, PN 515 (
http://www.mcc-hvac.com/wp-content/uploads/2014/03/Blowers.pdf)

http://www.gmcmhphotos.com/photos/i-need-more-air/p63445-img-0967.html

http://www.gmcmhphotos.com/photos/i-need-more-air/p63447-img-0969.html

The OEM fan and fan and fan duct will be removed and filled with aluminum
plate. The Hi, Med, and Lo wiring will be transferred to the new Blower
fan. BTW this fan already has Hi, Med and Lo hook ups with appropriate
resistance devices built in. In addition, all the dash controls are not
molested and will function as original. I plan to have a nice teak
enclosure with filters to cover the ugliness of the fan.

Any and all comments are required!



--
Regards,

Tom Pryor
4188 Limerick Dr
Lake Wales, Fl 33859
Cell 248 470 9186 <(248)%20470-9186>

Living on a waterfront is not a matter of life or death. Its more
important than that.
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

[Emery Stora]

Hi Tom
It looks great. There are several blowers with PN515(. Could you please give the full model number? The information in the ( ) was cut off.

Emery Stora

[Bruce Hislop]

Sounds good, but after removing the OEM fan and duct work, what about the defrost function? I'm not worried about winter time use, but in the summer
the windshield can get condensation especially during a heavy rainstorm.

Pulling smooth (laminar) airflow through the coils will work much better than pushing turbulent air as in the OEM configuration.
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
Hubler 1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

[Johnny Bridges via Gmclist]

My defroster was for chit anyway. I keep a towel on the instrument binnacle - it anchors the GPS too - and wipe as necessary.

--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

[Thomas Pryor]

I've had a few requests concerning my post. The GMC Photo site is very
cumbersome and I have used only once. VERY DIFFICULT TO SEQUENCE IMAGES, EH!

IF YOU ALL GO TO
http://www.gmcmhphotos.com/photos/i-need-more-air/p63443-hvac-blower-modification.html.
IT IS THE TITLE PAGE. ALWAYS TOGGLE TO THE LEFT & YOU WILL GET THE FULL
MONTY!

ALSO: Emery Stora, wanted more Info on the fan assy. If you go to this
PDF file, it is located on page 226 model 515 with brushes and internal
resistors, eh.
http://www.mcc-hvac.com/wp-content/uploads/2014/03/Blowers.pdf

[Guy Lopes]

Tom,

This is a great write-up! Thank you for posting it. What I haven't seen yet
is... how effective is it? Are you happy with the mod, and would you do
anything differently?

Thank you,

Guy Lopes
76 RB Birchaven
Sacramento, CA

-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of Thomas
Pryor
Sent: Monday, July 17, 2017 11:11 AM
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] WE ALL NEED MORE AIR

I've had a few requests concerning my post. The GMC Photo site is very
cumbersome and I have used only once. VERY DIFFICULT TO SEQUENCE IMAGES, EH!

[Emery Stora]

Thanks, Tom.
You might also want to post what model and year your GMC is. Different years had different venting of the air conditioner beneath the dash.

Emery Stora

[Bryan Hayes]

That squirrel cage is probably a lot quieter than the auxiliary cooler I have in the same spot.
--
Bryan Hayes
'76 Eleganza II
Salt Lake City, Utah

[Sammy Williams]

While "Vintage Air" doesn't make a "GMC motorhome" specific HVAC system,
they did write me to let me know they could use universal components that
they have to make a modern AC system for the GMC. I'd imagine it wouldn't
be to difficult to get them to look into a GMC dash system if there was
enough interest.

Barring that, I am sure the "Jims" can offer parts to make the GMC dash AC
work better, too.

(more options the better)

Sammy

[John Wright]

Sammy,
I bought the system from Jim K, actually I bought it from someone else who decided not to install it.

http://www.appliedgmc.com/prod.itml/icOid/849
or
http://www.appliedgmc.com/prod.itml/icOid/850

Works well with extensive rework and allows you to use the entire HVAC too.

JR Wright
GMC Great Laker MHC
GMC Eastern States Charter Member
GMCGL Tech Editor
GMCMI
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan

[John Wright]

That should read “without extensive rework”

JR

[Rob Mueller]

Bryan,

The problem with the aux coolers is that they have small diameter squirrel cage blowers (3" or 3.5") and to move enough air they
have to spin rapidly creating a lot of noise, I have one in Double Trouble.

I found a unit on eBay that came out of a mid 1960's Ford Mustang which has 5 inch blowers. I have not installed it yet but I did
spin it up and it was MUCH quieter.

Here's a photo showing the blowers:

Tiny URL: http://tinyurl.com/yaf368mv

Full URL:

https://www.google.com.au/search?q=mustang+air+conditioning+units&rlz=1C1NHXL_enAU731AU731&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUK
Ewjpx5HHwJHVAhUDHZQKHZMoC-UQsAQIQQ&biw=1280&bih=591#imgrc=N5F60NKHvDEi9M:

Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of Bryan Hayes
Sent: Tuesday, July 18, 2017 5:46 AM
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] WE ALL NEED MORE AIR

That squirrel cage is probably a lot quieter than the auxiliary cooler I have in the same spot.
--
Bryan Hayes

[Jim Kanomata]

Yes the squirrel cage will be quiet as it is drawing the inside air into
the system, BUT the air coming out of the registers will be noisy as your
uni, as there is turbulence coming through the ducts and grill.

--
Jim Kanomata
Applied/GMC, Newark,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502

[Bill Van Vlack]

Thomas,
This seems like a pretty straight forward modification to solve the (my) '76 non-recirc HVAC box issues if it will work with those boxes. Certainly
less of a mish-mash than other solutions. From the Jay Brand 'hot and cold' document, it seems like it might. Anxious to see how it performs in
service.
--
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; Since arrival: New HVAC blower, heat flap cable, headlight switch.

[Thomas Pryor]

After reviewing the available schematics of 73 Thru 78 all versions
supplymake-up air to the same location.
They all pressurize the box from a single squirrel cage fan located on the
side of the box.

MAKE UP AIR and VENTING were some of the major changes in 77/78, along with
other non- air related improvements. . Neither of these would be
impediments to this modification, IMHO.

The Modification that I am suggesting:

1. Pressurizes the box with makeup air from only one
source.........INSIDE RECIRCULATING AIR.


2. The air direction now enters thru the front of the box, in the most
advantageous direction. Air entering the OEM design has at least two
restrictions BEFORE reaching the A/C or heater coil. This MOD significantly
remedies that flaw.

3. The journey requires easily accessible items: A) Block off all
unused external HVAC box passages, B) make and install the necessary
duct work, C) hook up HI, MED & LOW from old wires Resister wires to the
new resistor pack on the MCC 515 fan/motor assy.
4. Nothing in the Dash control assembly requires any attention.

5. For those who have the a pre 77/78 with no Recirculation feature,
this becomes a major improvement.

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.

[Emery Stora]

Tom
The reason I asked what year you had modified was because my 1977 and most 1977 and all 1978s have a heat duct at the floor right in the center of the motorhome.
This appears to be right where you mount the blower motor. Does this still allow the 77-78 models to have the floor heat duct there?

Emery Stora
77 Kingsley
Frederick, CO

[Thomas Pryor]

E. Story wrote:
"The reason I asked what year you had modified was because my 1977 and most
1977 and all 1978s have a heat duct at the floor right in the center of the
motorhome.
This appears to be right where you mount the blower motor. Does this still
allow the 77-78 models to have the floor heat duct there?"

My coach is a 77 Birchaven. The floor duct is about 6" above the double
squirrel relocated fan. That said, a deflector attached to the passenger
side instrument panel directs air flow to passenger and driver location.
(Side Car) That deflector also prevents air flow to the area between the
seats where there are no occupants. Just say'n.

I PUT THIS DWG UP ON THE PHOTO SITE. HOPE IT HELPS
http://www.gmcmhphotos.com/photos/i-need-more-air/p63460-h-hvac-flow.html

[KB]

Hey Tom,
Where did you buy the blower? I'm not having much luck finding it online.

thanks,
Karen
1975 26'
Thomas Pryor wrote on Mon, 17 July 2017 11:10

> I've had a few requests concerning my post. The GMC Photo site is very
> cumbersome and I have used only once. VERY DIFFICULT TO SEQUENCE IMAGES, EH!
>
> IF YOU ALL GO TO
> http://www.gmcmhphotos.com/photos/i-need-more-air/p63443-hvac-blower-modification.html.
> IT IS THE TITLE PAGE. ALWAYS TOGGLE TO THE LEFT & YOU WILL GET THE FULL
> MONTY!
>
> ALSO: Emery Stora, wanted more Info on the fan assy. If you go to this
> PDF file, it is located on page 226 model 515 with brushes and internal
> resistors, eh.
> http://www.mcc-hvac.com/wp-content/uploads/2014/03/Blowers.pdf

[Jon Roche]

I did some searching

There are similar blowers on amazon:

https://www.amazon.com/gp/aw/d/B06XX9YLY1/ref=mp_s_a_1_22?ie=UTF8&qid=1501555275&sr=8-22&pi=AC_SX236_SY340_QL65&keywords=bus+blower+fan&dpPl=1&dpID=413y8OpY5YL&ref=plSrch

Maybe chinese knock off??? I do not know.

Down the road from me is a business that sells buses. They also sell truck accessories, and they are a dealer of the fan tom has listed. I have
not called and checked price and availability yet. Our local freightliner dealer is listed as well.
--
Jon Roche
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/

[KB]

I found some on ebay as well, but they seldom list the specs. The ones Tom found seem
to have pretty good CFM numbers, plus the three speed resistor pack we need (I think).
I've seen a bunch that have much lower CFM ratings.


lqqkatjon wrote on Wed, 02 August 2017 14:21

> I did some searching
>
> There are similar blowers on amazon:

thanks,
Karen
1975 26'

[John Phillips]

This looks like the real one on Amazon.com
search for:
"Mobile Climate Control 15-1556 Blower Motor"
but it cost $189 +15 shipping.

--

*John Phillips*

[KB]

Ok, I'm confused. Where did the 15-1556 number come from???
I only see 15-1561 as the likely number for the 3speed blower with resistor.
I'm not seeing 1556 anywhere in the document. What am I missing??

confusedly,
Karen
1975 26'


johnd01 wrote on Wed, 02 August 2017 17:09

> This looks like the real one on Amazon.com
> search for:
> "Mobile Climate Control 15-1556 Blower Motor"
> but it cost $189 +15 shipping.

[Jim Kanomata]

CFM is only half of the spec you must consider.
The pressure drop must be included.
The configuration of the box and the restriction of the coil can accumulate
pressure drop high enough to where the flow will be less than half.

--
Jim Kanomata
Applied/GMC, Newark,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502

[KB]

It looks like other brand blowers are easier to find.

Would this SPAL brand work? Or is it too many amps (not sure how to read their table):
http://www.jegs.com/i/SPAL/063/30006704/10002/-1?CAWELAID=230006180016449181&CAGPSPN=pla&CAAGID=15769068431&CATCI=pla-213811363271&CATARGETID=230006180037475786&cadevice=c&gclid=EAIaIQobChMIk6OHvIa61QIViYF-Ch0OdAXDEAQYASABEgKLL_D_BwE
or
https://tinyurl.com/yasoztnr
I think the OEM blower has a 30amp fusible link.

How about this one by RedDot:
http://www.partdeal.com/red-dot-dual-blower-motor-assembly-12v-with-resistor-73r5552-rd-5-8583-0p.html?zmam=74973193&zmas=1&zmac=4&zmap=77157575&gclid=EAIaIQobChMI8tmwgue51QIV0lYNCh3QVgmmEAkYCiABEgIUFvD_BwE
or
https://tinyurl.com/y83ss46z

thanks for any clues,

Karen
1975 26'

[John Phillips]

I did a google search and came up with an MCC document that listed it as 12
volt 3-speed blower then I found it on Amazon.com. There were CFM charts
with inches of water and current flow listed. I have looked but have not
found it again. The 13 and 3/4 inches seemed the same as well.

On Wed, Aug 2, 2017 at 7:00 PM, KB <ka...@sonic.net> wrote:

--

*John Phillips*

[Jim Kanomata]

Spal should publish the pressure drop/static pressure.
I'm guessing it needs to be at least .5 " wc.

--
Jim Kanomata
Applied/GMC, Newark,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502

[John Phillips]

Spal is listed in mmH20 and cubic meters per hour. 10 mm = 1050 CMH @32.5
amps Translates to about 0.4 inch h20 and 618 CFM and the 32.5 stays the
same.
Seems they are using a lot of power to get moderate air flow at a high
price.

--

*John Phillips*

[Rob Mueller]

Karen,

That SPAL blower is rated at 667 CFM.

Let's roughly calculate the internal volume of a 26 foot GMC: 25 feet X 8 feet X 7 feet = 1400 cubic feet

Lets guesstimate that blower is 50% efficient due to pressure drop through the mod Tom created; 1400 cubic feet divided by 330 means
that blower could replace all the air in a GMC in 4.24 minutes.

Seems like overkill to me.

Unless my logic and calculations are incorrect, which is quite possible.

Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of KB
Sent: Thursday, August 3, 2017 1:15 PM
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] WE ALL NEED MORE AIR

[John Phillips]

​I still think the 15-1556 is a good choice.​

--

*John Phillips*

[Keith V]

Overkill on the GMC aircon would be a first!

________________________________
From: Gmclist <gmclist...@list.gmcnet.org> on behalf of John Phillips <john.ph...@gmail.com>
Sent: Wednesday, August 2, 2017 11:27:06 PM

[Jim Kanomata]

Rob,
Good consideration, about the space.
Shows how one can miss things to consider.

On Wed, Aug 2, 2017 at 9:27 PM, John Phillips <john.ph...@gmail.com>
wrote:

--

Jim Kanomata
Applied/GMC, Newark,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502

[KB]

johnd01 wrote on Wed, 02 August 2017 20:25

> I did a google search and came up with an MCC document that listed it as 12
> volt 3-speed blower then I found it on Amazon.com. There were CFM charts
> with inches of water and current flow listed. I have looked but have not
> found it again. The 13 and 3/4 inches seemed the same as well.

That was the problem I kept running into online: I could find blowers I could buy, but no specs,
or I could find good specs in catalogs and such, but nowhere to buy them. I never could find any
good info about the MCC 15-1556 model, and at least one listing showed it as a 24 volt model.
Amazon doesn't say.

The CFM range in this form factor at 12 volts appears to be between about 150 and 800cfm.
The RedDot and Spal models look the same in the pictures; could be the same unit.
They can be had more easily and sometimes more cheaply than the MCC blower.
Overkill airflow would be a nice change as long as it's ok with the wiring in the coach.

Tom, if you don't mind my asking, how much was the unit you used? Where did you buy it?

thanks,
Karen
1975 26'

[John Phillips]

​I did see some specs for the 15-1556 before I found it on Amazon. As I
recall it was 14 amps max and 800 CFM at 1 inch of water. I will see if I
can find the data again. ​

--

*John Phillips*

[KB]

johnd01 wrote on Thu, 03 August 2017 10:11

> ​I did see some specs for the 15-1556 before I found it on Amazon. As I
> recall it was 14 amps max and 800 CFM at 1 inch of water. I will see if I can find the data again. ​

That would be awesome. FWIW, here's a really good page I found for the SPAL blower models:
http://www.spalautomotive.com/eng/products/centrifugal_12D.aspx

We're trying to figure out what the oem blower runs in terms of amps. The fusible link is 30 amps,
so has to run much less than that.

Also, what size is the oem blower wheel? I'm having trouble finding that info.
I think a double blower would be more efficient, but not if its wheels are too small.
Lots of trade offs here.

[James Hupy]

We were in a home improvement store a while back, and they had a floor
stand air mover that had no blades. Made no noise either. Don't know
exactly how it worked but seemed to move a whole bunch of air. Just an oval
shaped ring.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

[Rob]

https://en.wikipedia.org/wiki/Bladeless_fan <https://en.wikipedia.org/wiki/Bladeless_fan>

Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath

> On Aug 3, 2017, at 11:29 AM, James Hupy <james...@gmail.com> wrote:
>
> We were in a home improvement store a while back, and they had a floor
> stand air mover that had no blades. Made no noise either. Don't know
> exactly how it worked but seemed to move a whole bunch of air. Just an oval
> shaped ring.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403

[John Phillips]

To bad it does not list a 17-39-22
There are 3 blowers listing that I think could work
http://www.spalautomotive.com/eng/products/view_centrifugal.aspx?id=017-A40-73
http://www.spalautomotive.com/eng/products/view_centrifugal.aspx?id=017-A46-73
http://www.spalautomotive.com/eng/products/view_centrifugal.aspx?id=017-A54-73

--

*John Phillips*

[Jim Kanomata]

We need to determin feet per min. velocity through the Coil, as we know
anything over 500 ft/min face volocity can cause the condensate to blow
into the ducts and water droplets will be a problem. Having a 3-4 speed can
help avoid that to some degree.
If there is a way to find the data of our origional blower , it might guide
one to avoid problems.
We can take data off all the outlets and try to get approximate cfm it
produces at MAX.
Average Vel times the area of each and add them up. We have the
instruments, but now for me to do it.

On Thu, Aug 3, 2017 at 11:47 AM, John Phillips <john.ph...@gmail.com>
wrote:

--

Jim Kanomata
Applied/GMC, Newark,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502

[Joe Ricke]

Jim K and others,

Any idea the design capacity of the air conditioning system? Generally air conditions are designed to have 400 CFM through the evaporator per ton
(12,000 Btu/Hr).

This could help to estimate an airflow value.

Also, not sure what the surface area of the evaporator coil is, but using the typical 500 FPM value for velocity and multiplying by surface area
(square feet) will also give a ballpark value for required CFM.

Though, as has been stated previously, still need the pressure to select the proper sized blower to purchase.
--
Joe Ricke - KE0CPM
Arden Hills, MN
'77 Transmode

[Thomas Pryor]

The MCC Centrifugal Fan assembly (15-1561 )that I purchased some 2Yrs ago
was about $80. It is rated at 650 CFM with a static resistance of 3" H20.

I located a dealer that sells them for 80.57 plus shipping. See http://www.
buspartswarehouse.com/Products/A-C-Blower-Assemblies/2619902.html?whence=
Phone 800) 635-5567

*I AM TRYING TO GET A MORE RECOGNIZED SOURCE FOR THIS FAN.*.........DON'T
BE AFRAID OF SPAL OR OTHER RECOGNIZED NAMES THAT HAVE INTEGRAL RESISTORS.



FYI..................... THE MCC PART NO 15-1556 ON AMAZON IS A 24V
FAN.............DON'T DISAPPOINT YOUR YOUR SELF.

--
Regards,

Tom Pryor
4188 Limerick Dr
Lake Wales, Fl 33859

Cell 248 470 9186 <(248)%20470-9186>

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

[Rob Mueller]

Jim,

Agreed!

The problem with the GMC AC is the pressure drop through the whole system which is caused by the number of turns the air flow has to make. IIRC from my Hamilton Standard field rep days each 90° turn is like adding 5 - 7 feet of ducting. I can't remember how many turns it makes. This subject has been addressed here before as I vaguely remember stating this earlier.

Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of Jim Kanomata
Sent: Friday, August 4, 2017 5:48 AM
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] WE ALL NEED MORE AIR

[Rob Mueller]

Tom,

Your mod is quite clever, I was wondering why you didn't attach the blower directly to the back of the A/C plenum?

Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808


-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of Thomas Pryor
Sent: Friday, August 4, 2017 7:48 AM
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] WE ALL NEED MORE AIR

[Ken Henderson]

I'll answer that, based on my complete redesign & construction: First off,
in Tom's case, he didn't want to build a new HVAC box, which would be
required to provide room in front of the existing box for the blower.
He might, of course, have hung the blower below the box and only had one
bend in the air flow, but that would have partially obstructed the radiator.

Most importantly, for Tom's and My mods: The problem of providing supply
air to the blower. With the blower out front, where we'd really like it to
be for most-linear air flow, one would have to provide ducting from the
cockpit out to and completely surrounding the blower. A BIG fabrication
job.

If you look at all of the dual blowers, you'll see that they all induct air
to the wheels from both sides -- the outside and around the center-mounted
motor. I seriously consider closing the motor side and using round ducts
into each side, but finally figured out that the wheels would be seriously
starved for supply air.
Among other strikes against the idea.

Tom, feel free to supply your own reasons if this doesn't cover it.

Ken H.

On Thu, Aug 3, 2017 at 6:35 PM, Rob Mueller <robmu...@iinet.net.au> wrote:

> Tom,
>
> Your mod is quite clever, I was wondering why you didn't attach the blower
> directly to the back of the A/C plenum?

[jdli...@hotmail.com]

Here is a link to the blowers for $50
https://www.ctssurplus.com/products/mobile-climate-control-inc-engine-cooling-blower-p-n15-1556
--
JD Lisenby- USAF Ret
1978 Royale-455
Electromotive Tec2 FI & ignition

Navarre, FL

[Rob Mueller]

Ken,

I may be confused but doesn't Tom's design connect ducts from the floor to the BACK of the HVAC box?

My question meant to find out why not just bolt the blower directly to the back of the HVAC box?

Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808


-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of Ken Henderson
Sent: Friday, August 4, 2017 9:24 AM
To: GMC Mail List
Subject: Re: [GMCnet] WE ALL NEED MORE AIR

[Ken Henderson]

We may be referring to different "backs" -- to me, that means the forward,
outside, surface of the HVAC box -- in other words, nearest the front of
the coach.

The blower is inside the cockpit, so it's inducting air from there rather
than having to have it ducted to a location on the outside of the HVAC box.

Ken H.

On Thu, Aug 3, 2017 at 8:21 PM, Rob Mueller <robmu...@iinet.net.au> wrote:

> Ken,
>
> I may be confused but doesn't Tom's design connect ducts from the floor to
> the BACK of the HVAC box?
>
> My question meant to find out why not just bolt the blower directly to the
> back of the HVAC box?
>
>

[Rob Mueller]

Ken,

Let's use aircraft terms.

I think Tom's blower mod feeds air to the tail end of the HVAC box.

http://www.gmcmhphotos.com/photos/i-need-more-air/p63444-ab-thumb-img-0955-1024.html

Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808


-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of Ken Henderson
Sent: Friday, August 4, 2017 11:02 AM
To: GMC Mail List
Subject: Re: [GMCnet] WE ALL NEED MORE AIR

We may be referring to different "backs" -- to me, that means the forward,
outside, surface of the HVAC box -- in other words, nearest the front of
the coach.

The blower is inside the cockpit, so it's inducting air from there rather
than having to have it ducted to a location on the outside of the HVAC box.

Ken H.

[John Phillips]

We need someone to get some data on how well this works. Air flow and
temperature differential temperature. If the evaporator is not cold it does
not matter how much air you push if you are counting on cooling. If you are
counting and having fast moving 100-degree air, well that is a different
story.

--

*John Phillips*

[Rob Mueller]

John,

The compressor / evaporator have more than enough capacity. The problem is air flow.

What year GMC do you have?

[Thomas Pryor]

So OKAY, just occurred to me that the modification also has a significant
increase in Square inches of inlet size.

The opening on the side of the HVAC box has an effective size 5" X 3.5" or
17.5 Sq inches.

Cutouts for the double centrifugal into 4" X 3.5" X two or 28 square
inches.

I believe that works out to be about a 35% increase, just say'n

____________________________________________________________
________________________________________________

FOR GENERAL COMPARISON ........BUT CERTAINLY NOT SCIENTIFIC..........ORDER
OF MAGNITUDE COMPARISON:

SPAL makes a 3 speed single impeller (PN SPAL 064 A42 28 D 12V 3 SPEED
BLOWER) SEE (http://www.spalautomotive.com/eng/products/centrifugal_12S.aspx
)

I think itis comparable to our OEM SINGLE IMPELLER BLOWER.............. IT
IS RATED AT 455 CFM


SPAL INLET is 4 3/4" or 19 SQ INCHES GMC INLET is 4
1/2 " 17.3 SQ INCHES

SPAL OULET IS 5 3/4" X 2 5/8" or 15 SQ INCHES GMC OUTLET IS 5" X 3.5"
OR 17.5 SQ INCHES

SPAL IMPELLER IS 4.8 INCHES DIA GMC IMPELLER IS
5.0 INCHES DIA

SPAL IMPELLER IS 3.9 INCHES WIDTH GMC IMPELLER IS 3.25
INCHES WIDTH

I THINK WE COULD MAKE THE STATEMENT THAT OUR GMC BLOWER EFFECTIVELY
DEVELOPS 450 TO 500 CFM.
THAT SAID THE MCC 15-1561 DOUBLE BLOWER IS RATED AT 650 CFM PER MY CONTACT
AT MCC, JOSH.

THAT IS A 23 % IMPROVEMENT, EH?

_______________________________________________________________________________________________________________

IT WOULD APPEAR THAT THIS MODIFICATION INCREASES HVAC INLET SIZE BY 35%
AND A 23 % CFM INCREASE........JUST SAY'N

__________________________________________________________________________________________________________________

BTW Just found one more source on Bay for the MCC 151561 blower at $89.00
http://www.ebay.com.sg/itm/MCC-12V-Dual-Squirrel-Cage-Twin-Blower-Fan-Motor-
Assy-15-1561/250875055779
--

--
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.

[Ken Henderson]

Yep, I agree. And so do I. Simply because its too difficult to route
"return air" to a blower at the nose end of the HVAC box.

Ken H.

[KB]

Thomas Pryor wrote on Thu, 03 August 2017 18:51

> BTW Just found one more source on Bay for the MCC 151561 blower at $89.00
> http://www.ebay.com.sg/itm/MCC-12V-Dual-Squirrel-Cage-Twin-Blower-Fan-Motor-
> Assy-15-1561/250875055779

alas, 0 available :(

[KB]

SpookyEng wrote on Thu, 03 August 2017 16:54

> Here is a link to the blowers for $50
> https://www.ctssurplus.com/products/mobile-climate-control-inc-engine-cooling-blower-p-n15-1556
>

> Some other pictures I looked at on this blower showed it could be hooked up as 6, 12 or 24v just a different flag connector.


I saw that one earlier but didn't buy it because it didn't seem to have the three speed resistor pack on it;
not sure what all the wiring and such is in the picture.

Karen
1975 26'

[Thomas Phipps]

Adding a resistor package is a trivial obstacle. Probably be able to acquire one easily at any men's mall. Nothing special.
More fun would be a PWM module and really control the speed to exactly what you need.
Doing the 'pin out' on the cable would be interesting, but I think you would want to roll your own design.
Tom, MS II
1975 Avion sale
--
1975 GMC Avion
KA4CSG

[Matt Colie]

I knew it was something....

Since Tom and I first talked about this, something kicked up a parity error flag and it has taken me a while to track it down...

Where Tom put blowers is where 73&4 have the MAX AIR outlet part tacked on. That piece it essential if one is to have any A/C performance at all in
the older coaches.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

[KB]

Matt Colie wrote on Fri, 04 August 2017 05:32

> I knew it was something....
>
> Since Tom and I first talked about this, something kicked up a parity error flag and it has taken me a while to track it down...
>
> Where Tom put blowers is where 73&4 have the MAX AIR outlet part tacked on. That piece it essential if one is to have any A/C performance at all
> in the older coaches.
>
> Matt

We have a 75 with the 'max air' opening and the goofy scoop thing to direct it upwards from the floor.
Since that's what we use 99% of the time, it was a concern for me too.
There seems to be enough room between the scoop and the engine hatch opening, and I was also considering partially recessing
the blower into the floor to make it less of a giant lump. If you don't have the scoop though,
you'd risk having all your AC output being sucked back into the intake of the new blower.

Looks like it's still workable to me.

I was just comparing this to the other modification, where you mount the OEM blower on the front side of the case.
The problem with that is it's sucking air through the evap instead of blowing it, and we were concerned about
the water/vapor going through the blower motor. Short of a major rework or replacement of the enormous OEM box,
Tom's idea looks like a good improvement.

Karen
1975 26'

[John Phillips]

Has anyone finished and tested this mod?

--

*John Phillips*

[KB]

johnd01 wrote on Sat, 05 August 2017 19:36

> Has anyone finished and tested this mod?

Just got my blower in the mail today and hope to try the mod in the next few days.

[KB]

KB wrote on Wed, 09 August 2017 19:25

> johnd01 wrote on Sat, 05 August 2017 19:36
> > Has anyone finished and tested this mod?
>
>
> Just got my blower in the mail today and hope to try the mod in the next few days.
>
> Karen
> 1975 26'

Well, not as good as I hoped. I chose to try abandoning the max air vent, so mounted the new blower
directly on the back of the AC box. I thought about mounting it further back and keeping the max air vent "snorkel",
but I didn't want that much protrusion into the cockpit. Without the max air slot open, it's basically the
same as the 73/74 box

We have an anemometer for measuring wind speed, so for lack of a better tool, I used that. All measurements
were taken with AC blower set to "high". The stock system with the max air vent closed got about 2 meters
per second (mps) out of the center dash vents. With the new blower, they got 3mps. The stock max air duct vents with
the oem blower got about 6mps, so double even the improved center vents. With no duct in front of the max air slot, it's 9+mps.

So, with the new blower, there was a definite improvement out of the center dash vents, though still nothing out of
the passenger side vent. However, it was nowhere near as good as the max air vent with the stock blower. There's also
the issue of the blower noise, though that could likely be improved upon with a baffle.

I think Mark Wall pretty well summed it up in his presentation, when he said
it wouldn't matter how much air you push through it, the oem (pre-77) ducts are the problem.
He did quite an interesting bunch of modifications, if you haven't seen them:
http://www.gmcmi.com/wp-content/uploads/2013/02/HVAC-Systems.pdf

FWIW, I was able to use the stock resistor pack with the new blower. Slightly easier
than modifying the wiring to use the new resistors, though that's not bad either.
The oem resistors are about half the ohms of the new pack.
Since I was only measuring "high", it didn't matter.

I'll probably play with this more later, but for now I'm out of time.
If I can get the heater core out, I think I could do Mark Wall's vent modifications
without removing the whole AC box.

[Johnny Bridges via Gmclist]

I'll point out for those of us attending the December in Orlando Pet The Puppy And Spend Money rally at Wekiwa Springs, they day trip to SkyCraft
should produce workable blowers for this mod. The have an aisle of them in various configurations.
Ten sites left in the favored loop, 21 total available out of 60 total. Book early or be left out.
--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

[Jon Roche]

You said you mounted it differerntly then Tom? Can you post a picture?

I have a 75, and I just cant put my thoughts around the max air vent. Mine has a large floor ioening that I would consiter the recirc opening.

Sometime before next spring I am really going to have to test and learn what the vacuum flapper vents are supposed to do, and start there. I still
plan on adding a aux evaporator, but having the oem working better would allow more ease and obviously help heat/defrost side.

I also wonder if maybe there are mouse nests one cannot see. I know in a 91 f-150 they can clog up vents that you never knew existed. I have had
the front of my hvac box opened in the past year and cleaned things up and replaced the gasket on the heat/ac flapper.
--
Jon Roche
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/

[KB]

lqqkatjon wrote on Tue, 15 August 2017 07:06

> You said you mounted it differerntly then Tom? Can you post a picture?
>
> I have a 75, and I just cant put my thoughts around the max air vent. Mine has a large floor ioening that I would consiter the recirc opening.
>
>
> Sometime before next spring I am really going to have to test and learn what the vacuum flapper vents are supposed to do, and start there. I
> still plan on adding a aux evaporator, but having the oem working better would allow more ease and obviously help heat/defrost side.
>
> I also wonder if maybe there are mouse nests one cannot see. I know in a 91 f-150 they can clog up vents that you never knew existed. I have
> had the front of my hvac box opened in the past year and cleaned things up and replaced the gasket on the heat/ac flapper.

I believe the "max air" slot change was done sometime in 75, maybe pretty late. There was also a kit available, which I think basically
did the max air modification to existing boxes. If you have no air coming out of that bottom slot with the controls set all the way to the left
on "recirc", either the vac control to the max air door is broken, or you have the earlier style box, which uses the big slot below the dash as a
recirc intake.
If you have the max air version, there will be a flapper door just inside the slot on the left 12" or so, and the old vacuum pot for the recirc door
on the blower side of the box is used to operate the max air door.

Without the max air slot, either moving the old blower to the front of the box as Mark Wall did, or installing the new blower as Tom did, would
improve your airflow somewhat. Unfortunately, the real problem is the ducting.

Anyway, here are pics of my installation directly on the back of the ac box, right in front of the slot below the dash.
In that position, the recirc slot would basically become a fresh air intake for the blower when the outside "recirc" door is open:
http://www.gmcmhphotos.com/photos/hvac-original-and-mods/p63546-new-blower-arrangement.html
http://www.gmcmhphotos.com/photos/hvac-original-and-mods/p63548-new-blower-arrangement.html
http://www.gmcmhphotos.com/photos/hvac-original-and-mods/p63547-new-blower-arrangement.html

Look at the the diagrams in my album as well as the pictures of various boxes and you should get a much better understanding.
One caveat: in Brand's "Separating Hot from Cold", he basically drew the 77/78 duct plenum on all the boxes. For the earlier boxes,
the vacuum controlled doors are spread around the dash, inside and out, and there's no plenum on the cockpit side of the box.

hth,
Karen
1975 26'