Home » Public Forums » GMCnet » [GMCnet] CFM for AC Blower and Mod to the System??
| [GMCnet] CFM for AC Blower and Mod to the System?? [message #125091] |
Sun, 08 May 2011 15:01  |
Arthur Mansfield
Messages: 290
Registered: April 2010
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I am trying to understand the engine AC system. I have found the schematic for the vent system. I am thinking about using the modification where they adding two additional event from the front of the AC box like others have done (I will be using 3 inch instead of 2 inch). I was going to add an in line blower in each line of 165 CFM each (http://replacementboatparts.com/3bilgeblower.aspx). So I was wondering what the CFM was for the blower in the AC box rated CFM. I could add 225 CFM if that is required but then I have real space problems. Each added blower will be controlled by a variable resistant switch which is rated at 3 times the current draw for the motor. Not sure the switch I am planning to use will work for motor controller (http://replacementboatparts.com/switchesandbreakers.aspx).
Assuming loses the 165 blower would give about 12 ft per sec air flow from a 3 inch vent with no air flow from the air box. This would replace the air in the RV about once every 6 minute assuming some loses. The air flow should be better than that since there will pressure on the in line motor. Those who use this set-up with the in line bower have good air flow thru a 2 inch line but require extra cooling on real hot days. So I am hoping the in line would add enough flow to cool the RV even on hot days.
What would happen if I blew back into the vent system where I could enter from the front side where the air comes in from the vent system (back side in my definition). It looks like it would work for the passenger side but not for the drives side.
Has anyone tried this type mod on adding in line blowers. This would allow some separate control on each side as to how the blowers are set.
Art & Doris
76 EL
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| Re: [GMCnet] CFM for AC Blower and Mod to the System?? [message #125093 is a reply to message #125091] |
Sun, 08 May 2011 15:33  |
James Hupy
Messages: 6806
Registered: May 2010
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As I recall from my GM A/C training, there is an ideal air flow rate for the
amount of refrigerant that is in the system. If you exceed that ideal, the
heat exchange doesn't have time to occur. Many systems indicate cooler
temperatures at discharge air vents using medium fan speed than using high
speed. If you stray too far away from the ideal, you could have a system
that moves a bunch of air that is not as cool. You did not say what year
coach you have. The early ones had a poorly performing HVAC system compared
to the later ones, and that is the ones that have been modified extensively
to improve performance. What seems to work the best is to add more cooling
coils in addition to increased air flow, and some work on the vacuum motors,
shutter seals, and hot water bypasses. Lots of clever people out there in
GMC land who have come up with innovative work arounds for the earlier
coaches. Most of them are more than willing to share with others.
Jim Hupy
Salem, Or
78 GMC Royale 403 ( we need heaters here more than A/C)
On Sun, May 8, 2011 at 1:01 PM, 1104agm <1104agm@gmail.com> wrote:
> I am trying to understand the engine AC system. I have found the schematic
> for the vent system. I am thinking about using the modification where they
> adding two additional event from the front of the AC box like others have
> done (I will be using 3 inch instead of 2 inch). I was going to add an in
> line blower in each line of 165 CFM each (
> http://replacementboatparts.com/3bilgeblower.aspx). So I was wondering
> what the CFM was for the blower in the AC box rated CFM. I could add 225
> CFM if that is required but then I have real space problems. Each added
> blower will be controlled by a variable resistant switch which is rated at 3
> times the current draw for the motor. Not sure the switch I am planning to
> use will work for motor controller (
> http://replacementboatparts.com/switchesandbreakers.aspx).
>
> Assuming loses the 165 blower would give about 12 ft per sec air flow from
> a 3 inch vent with no air flow from the air box. This would replace the air
> in the RV about once every 6 minute assuming some loses. The air flow
> should be better than that since there will pressure on the in line motor.
> Those who use this set-up with the in line bower have good air flow thru a
> 2 inch line but require extra cooling on real hot days. So I am hoping the
> in line would add enough flow to cool the RV even on hot days.
>
> What would happen if I blew back into the vent system where I could enter
> from the front side where the air comes in from the vent system (back side
> in my definition). It looks like it would work for the passenger side but
> not for the drives side.
>
> Has anyone tried this type mod on adding in line blowers. This would allow
> some separate control on each side as to how the blowers are set.
>
>
> Art & Doris
> 76 EL
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] CFM for AC Blower and Mod to the System?? [message #125096 is a reply to message #125094] |
Sun, 08 May 2011 16:11 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Instead of using rheostats for motor speed control, use Pulse Width Modulation (PWM) for an accurate speed control, infinite speeds and little or no displaced heat. Easy to build, easy to install. Check ads in "Nuts and Volts" magazine.
Tom Phipps, 8 days to GMC
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: [GMCnet] CFM for AC Blower and Mod to the System?? [message #125110 is a reply to message #125091] |
Sun, 08 May 2011 18:15 |
idrob
Messages: 645
Registered: January 2005
Location: Central Idaho
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| Arthur Mansfield wrote on Sun, 08 May 2011 13:01 |
I am trying to understand the engine AC system. I have found the schematic for the vent system. I am thinking about using the modification where they adding two additional event from the front of the AC box like others have done (I will be using 3 inch instead of 2 inch). I was going to add an in line blower in each line of 165 CFM each
(snip)
Art & Doris
76 EL
|
It has always been my feeling that the original cooling coil size was simply not large enough to allow proper cooling for a coach of this size. Add to that the poor air path and the sum total is a very marginal cooling system on models up to 1977. There were several changes after that which made the system better, from all reports.
But, although several people have shown that increased air flow will help in the earlier coaches, the original evaporator coil is just too small (again, my opinion). The best remedy is a second evaporator, which many have added with excellent results. I know if I still had my coach, that is what I would have done, rather than trying to make extensive modifications to the original air path or volume.
No matter what I did with my 76, type 2 system, when the outside temp was high, the output temperature from the vents went up substantially. That indicated to me that the evaporator simply did not have the capacity to cool the air to a low enough temp with higher input temps, due to it's marginal size. More air flow will not change this issue.
The original compressor and condenser will easily support a second evaporator. The big bottleneck is the undersized evaporator coil in the earlier units as they came from the factory.
(judgement and opinion shut down now, grin).
Rob Allen
former owner of '76 x-PB
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| Re: [GMCnet] CFM for AC Blower and Mod to the System?? [message #125155 is a reply to message #125110] |
Mon, 09 May 2011 00:50 |
Arthur Mansfield
Messages: 290
Registered: April 2010
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I was originally thinking of adding a second system. I thought this mod would be a simple addition to try since those who just added the extra vents claimed to havr obtain good results except it would not cool the hole coach on hot days. If the coil is to small then what I was proposing will not work but it would take long to find out. Now I have been told that the system would cool the hole RV if the air flow was improved by someone who had done other mod's. I guess I could ger out my old heat transfer and run some numbers and find out but it sure has been a long rime since did any off that kind of computing.
I would sill like to konw what the CFM of the original blower is. That would give me an idea of what of what the flow rate was supposed to be thru the coils.
Thanks
Art & Doris
76 El
On May 8, 2011, at 6:15 PM, Rob Allen wrote:
>
>
> Arthur Mansfield wrote on Sun, 08 May 2011 13:01
>> I am trying to understand the engine AC system. I have found the schematic for the vent system. I am thinking about using the modification where they adding two additional event from the front of the AC box like others have done (I will be using 3 inch instead of 2 inch). I was going to add an in line blower in each line of 165 CFM each
>>
>> (snip)
>> Art & Doris
>> 76 EL
>
>
> It has always been my feeling that the original cooling coil size was simply not large enough to allow proper cooling for a coach of this size. Add to that the poor air path and the sum total is a very marginal cooling system on models up to 1977. There were several changes after that which made the system better, from all reports.
>
> But, although several people have shown that increased air flow will help in the earlier coaches, the original evaporator coil is just too small (again, my opinion). The best remedy is a second evaporator, which many have added with excellent results. I know if I still had my coach, that is what I would have done, rather than trying to make extensive modifications to the original air path or volume.
>
> No matter what I did with my 76, type 2 system, when the outside temp was high, the output temperature from the vents went up substantially. That indicated to me that the evaporator simply did not have the capacity to cool the air to a low enough temp with higher input temps, due to it's marginal size. More air flow will not change this issue.
>
> The original compressor and condenser will easily support a second evaporator. The big bottleneck is the undersized evaporator coil in the earlier units as they came from the factory.
>
> (judgement and opinion shut down now, grin).
>
>
>
> --
> Rob Allen
> former owner of '76 x-PB
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| Re: [GMCnet] CFM for AC Blower and Mod to the System?? [message #125185 is a reply to message #125155] |
Mon, 09 May 2011 09:20 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Art,
There is another problem with the system - Delta P - the airflow makes
numerous 90 degree bends that really kills the airflow.
I'm probably wrong but I think it's seven by the time it heads out the
vents.
Steve Ferguson made a presentation on the system at Pueblo.
Regards,
Rob M.
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of 1104agm
Sent: Monday, May 09, 2011 1:50 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] CFM for AC Blower and Mod to the System??
I was originally thinking of adding a second system. I thought this mod
would be a simple addition to try since those who just added the extra vents
claimed to havr obtain good results except it would not cool the hole coach
on hot days. If the coil is to small then what I was proposing will not
work but it would take long to find out. Now I have been told that the
system would cool the hole RV if the air flow was improved by someone who
had done other mod's. I guess I could ger out my old heat transfer and run
some numbers and find out but it sure has been a long rime since did any off
that kind of computing.
I would sill like to konw what the CFM of the original blower is. That
would give me an idea of what of what the flow rate was supposed to be thru
the coils.
Thanks
Art & Doris
76 El
On May 8, 2011, at 6:15 PM, Rob Allen wrote:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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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] CFM for AC Blower and Mod to the System?? [message #125272 is a reply to message #125110] |
Mon, 09 May 2011 18:33 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
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I just have to wonder, if the evap coil is too small, in your opinion, then why have some of the GMC guys been able to get cooling temperatures and supposedly cool the coach, by making modifications to everything but the evap coil????
It is my thought, that the evap coil is enough for the drivers area, if you want to cool the rear, you need a remote coil and fan as you would with any larger vehicle. Did GM offer one as an add on???
I think too many have made revisions without changing the evap coil and had very good results to be concerned with the size of the evap coil.
It just one of those " if it works, then its right " deals.
Gatsbys' CRUISER  08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
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| Re: [GMCnet] CFM for AC Blower and Mod to the System?? [message #125274 is a reply to message #125185] |
Mon, 09 May 2011 18:37 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
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There is another problem with the system - Delta P - the airflow makes numerous 90 degree bends that really kills the airflow.
_____________________________________________________-
Of the HVAC changes one of our " Owner / Specialists " have made was to add a curve where the air needs to be persuaded to turn. As I recall, This made a very big difference in the airflow of the system.
Gatsbys' CRUISER 08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
_
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| Re: [GMCnet] CFM for AC Blower and Mod to the System?? [message #125278 is a reply to message #125229] |
Mon, 09 May 2011 18:43 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
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I would be careful with the bilge blowers. They are a direct flow type of blower, with fan blades, not the squirrel cage that the GMC fitted blower has. The Squirrel cage can build enough pressure to force the air through the evap coil and system where the bilge blowers do not have that pressure to push the air through a bunch of bends, a evap coil, heater coil, more bends, skinny air duct, doors and out the vents. It is a different application for the bilge blowers. Knowing the GMC hvac system and its hi resistant pathways, I would venture to say, the bilge blower will not be satisfactory....
My thought
Gatsbys' CRUISER 08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
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