| OEM roof top AC question [message #97824] |
Mon, 30 August 2010 16:19  |
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Tom Fort
Messages: 51
Registered: January 2004
Karma: 0
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I had a 4k onan and one oem rooftop AC. I'm thinking about getting a generator to use on the road for just the rooftop AC. I'm considering one of those platforms that attach to the trailor hitch and the cheapest generator possible.
Howmany watts are required to startup and run the rooftop AC?
Thanks for any input.
Tom
Tom Fort, KA4KGR
73 Painted Desert, Family owned Since 1973
Lugoff, SC
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| Re: OEM roof top AC question [message #97837 is a reply to message #97824] |
Mon, 30 August 2010 17:51  |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Tom, the big load will be the starting of the A/C. My 3 Kw will not start the either of the OEM A/C's on my coach. Further back there is a discussion about "supercapacitor" for starting the A/C, that may be a solution. I would see if I could borrow a generator from a friend, before I ever committed to purchasing one. I have seen a generator mounted on a rear hitch, as you have mentioned. Might think of a remote start.
Why not just run the Onan? It is already wired in to the coach, and it is plumbed to the GMC gas tank. The Onan can be made to work if it is being stubborn.
Tom Phipps,
whom you helped with a cooling problem
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: OEM roof top AC question [message #97839 is a reply to message #97824] |
Mon, 30 August 2010 18:13 |
idrob
Messages: 645
Registered: January 2005
Location: Central Idaho
Karma: 0
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| Tom Fort wrote on Mon, 30 August 2010 14:19 |
I had a 4k onan and one oem rooftop AC. I'm thinking about getting a generator to use on the road for just the rooftop AC. I'm considering one of those platforms that attach to the trailor hitch and the cheapest generator possible.
Howmany watts are required to startup and run the rooftop AC?
Thanks for any input.
Tom
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Look at the nameplate on the AC, you will see the running amps (usually about 13.5 to 15, and the FLR amps (full locked rotor). The FLR is the MAXIMUM starting amps the AC will need. However it is for only a few seconds, and most conventional (not inverter) generators will have enough running inertia and internal copper to start a single AC if rated over 3000 to 3500 watts. Inverter generators are a bit more problematical, starting things.
The best new AC units can be purchased with only a 10 amp running current and produce the same 13,500 btuh that the original unit put out. They are the high efficiency units, but I assume you are not going to replace your AC. For anyone else reading this, I think the high efficiency units are the best thing to purchase if you are doing a replacement. They start easier, and take about 25 to 30% less energy to produce the same cooling. Cost is about an extra $50 over the price of the conventional inefficient ones.
You may or many not be very happy with the "cheapest generator possible" due to noise, short life, and a bunch of other issues, but that is your choice. Most are single cylinder, built to a price, and limited to a short life of only a few hundred hours.
I believe Randy in Phoenix has done what you want to do, you might want to contact him directly. I think, however, he located another 4 Kw unit for his original generator compartment. I am sure he will let you know.
Hope this helps some, Just my thoughts and opinions.
Rob Allen
former owner of '76 x-PB
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| Re: [GMCnet] OEM roof top AC question [message #97860 is a reply to message #97838] |
Mon, 30 August 2010 20:08 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Tom,
It might be better to add an additional evaporator under the GMC's dash. The
compressor will easily handle the extra load.
Google Vintage Air.
Regards,
Rob M.
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Tom Fort
Sent: Monday, August 30, 2010 6:59 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] OEM roof top AC question
Hey Tom. Sorry, but after spending hundreds on the old onan, it is in the
scrap yard. I'm just looking for the least expensive way to have cooling
while driving. We already rebuilt the original dash air system but need
more cool air.
--
Tom Fort, KA4KGR
73 Painted Desert, Family owned Since 1973
Lugoff, SC
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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] OEM roof top AC question [message #97902 is a reply to message #97901] |
Tue, 31 August 2010 06:34 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Tom,
Evaporative cooling is suited for climates where the air is hot and
the humidity is low, primally in the western and mountain states. In
your state the unit would act more as an humidifier and have little or
no cooling. Not really a good choice for a motorhome.
JR Wright
On Aug 31, 2010, at 7:11 AM, Tom Fort wrote:
>
>
> What is the cost of an evaporator? Also, where are they available?
>
> --
> Tom Fort, KA4KGR
> 73 Painted Desert, Family owned Since 1973
> Lugoff, SC
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] OEM roof top AC question [message #97945 is a reply to message #97901] |
Tue, 31 August 2010 13:19 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| Tom Fort wrote on Tue, 31 August 2010 04:11 |
What is the cost of an evaporator? Also, where are they available?
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For used items you should be able to find something at the Men's Mall (Junk yard, U-pick-it or the like) from the rear of a passenger van.
New items can be found at either of the Jims <http://www.appliedgmc.com/prod.itml/icOid/850> Vintage Air, or other similar locations.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: OEM roof top AC question [message #97971 is a reply to message #97824] |
Tue, 31 August 2010 16:09 |
zhagrieb
Messages: 676
Registered: August 2009
Location: Portland Oregon
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My coach has a 2800 watt Onan that runs the original rooftop AC and the microwave at the same time.
Glenn Giere, Portland OR, K7GAG
'73 "Moby the Motorhome" 26'
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| Re: OEM roof top AC question [message #97982 is a reply to message #97971] |
Tue, 31 August 2010 17:27 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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| Glenn Giere wrote on Tue, 31 August 2010 14:09 |
My coach has a 2800 watt Onan that runs the original rooftop AC and the microwave at the same time.
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Do you have a model number of the Onan? I suspect it is NOT an inverter model. It might be a good thing for 23 foot owners to know.
I am also thinking your AC is different in some way... reducing starting current draw.
Newer. more efficient air conditioners should start on a fairly small gen-set -- as along as it it a "true" AC generator. (Inverter models need to be a little larger.) Once the AC is running it should support an additional load... until the AC cycles!
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: OEM roof top AC question [message #98012 is a reply to message #97982] |
Tue, 31 August 2010 21:54 |
zhagrieb
Messages: 676
Registered: August 2009
Location: Portland Oregon
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I couldn't believe it either first time I tried. The AC I believe is vintage '73. The temp was set on coldest so the compressor did not cycle, that's the biggest load. The Onan is a Microlite 2800.
Glenn
Glenn Giere, Portland OR, K7GAG
'73 "Moby the Motorhome" 26'
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| Re: OEM roof top AC question [message #98024 is a reply to message #98012] |
Wed, 01 September 2010 05:31 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| Glenn Giere wrote on Tue, 31 August 2010 19:54 |
I couldn't believe it either first time I tried. The AC I believe is vintage '73. The temp was set on coldest so the compressor did not cycle, that's the biggest load. The Onan is a Microlite 2800.
Glenn
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Glenn,
Sounds good. A/C and microwave... Do you REALLY need much more out a generator?
I did some research on the MicroLite generator. Found this statement:
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The 2.8 KV genset will start and run one approved 13,500 Btu air conditioner (14.7 cooling amps or less) plus a 600 W baseload, or one approved 11,000 Btu air conditioner plus a 900 W baseload.
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Is this a 23 foot or 26 foot coach? They say it is 24"L x 16.44"W x 12.25"H. I THINK it is a little long for a 23 foot generator bay without modifications. They (Onan) makes a little smaller one with an external muffler (19.6L x 16.7"w x 12.3"H) It is marketed as a "Camppower." Looks like the main difference is the muffler. (Not sure on that... )
Reviews on the MicroLite seems to be mixed. (They love it or hate it.) I have found them listed used for $500 to $1500. New from $2,185 <http://www.coloradostandby.com> +$200 flat rate shipping and you'll need and installation kit.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: OEM roof top AC question [message #98050 is a reply to message #98024] |
Wed, 01 September 2010 10:23 |
zhagrieb
Messages: 676
Registered: August 2009
Location: Portland Oregon
Karma: 0
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My 2800 has given no problems over the several years I've owned the coach. I'd suggest the external muffler version as it exhausts downward at the front right corner so is easier to access if you have to remove the unit. Mine has the muffler inside and exits in the rear so I must crawl under and undo the exhaust pipe before I can remove it. (Only had to do that once.) Only trouble I've had is starting after a long sit. I have to start it at the unit and "tickle" the throttle manually till it catches. After that remote starts are OK.
Glenn Giere, Portland OR, K7GAG
'73 "Moby the Motorhome" 26'
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