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  1. #1

    Default Air Conditioning Options with the engine off


    I am looking into buying a gmc or chev full size van, AWD. One of the purposes of the van is a "portable office", meaning that I will be routinely using it during hot weather. It would be handy to have at least 2 - 4 hours of AC with the engine off, if possible.

    I would like to find an alternative to having to run the engine to get a/c. Sometimes I will be stationary near 110v power, sometimes not. Some ideas that came to mind for me are:
    - Move the AC compressor so it runs off of a 12V motor / big battery combo.
    - Some kind of "rear only" ac unit that is separate from the engine
    - Large inverter + some kind of 110v ac unit (least desired)

    I am open to options, but I prefer to not have to consume large amounts of interior space to pull it off, if possible.

    Any ideas / thoughts are welcome.



  2. #2
    stephan's Avatar
    Join Date
    Sep 2010
    Far West, Oregon USA,
    Blog Entries


    Welcome to the GM truck club Harry. Sorry I don't have any ideas for you but this site is populated with some highly knowledgable people so I'm sure somebody will be able to help you.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol

  3. #3


    My first reaction was no way, you would need a bank of 10 golf cart batteries to run an AC for a couple of hours. Then I started doing some math.

    Let's start with a small window style AC unit, 5000 BTUs.

    Draws 515 watts, 4.8 amps @ 120 volts. That converts to about 50 amps at 12 volts. But we need an inverter, and a big one.

    Here's one that would likely work.

    1/3 load efficiency is 85%, so that means we need about 60 amps feeding the inverter.

    Typical group 27 deep cycle battery has an Amp/Hour rating of 90. So that means one Group 27 could run that AC for an hour and a half, in theory. As you increase the current draw, the amp/hour rating decreases. So two batteries could likely give you two hours, three batteries three hours.

    Here's a good read on deep cycle batteries.

    Dollars and sense......

    Three Group 27 batteries - $300
    Decent inverter - $300
    Wiring, isolator, etc. $200

    And you still need a way to recharge the batteries. Your stock 105 amp alternator is not going to be too happy with that situation for long. You would need to upgrade to a beefy alternator, or install a second alternator.

    Said and done, you could spend close to a grand getting setup. You might be better off buying a 2000W Honda suitcase generator for not much more money.
    Last edited by 2COR517; 10-31-2010 at 06:51 PM.
    When you hear hoofbeats, look for horses not zebras.

  4. #4


    Thank you for the welcome and replies. Your power rating numbers are very close to what I was thinking as well, and as you noted, it is really pushing some power from a battery. Perhaps my run time number goal is too high from batteries.

    I hope you guys don't mind if I just ramble a bit in this thread and collect info / thoughts / configuration related stuff in it.

    I have seen 4 - 5 kw inverters from the solar energy market, but they were intended for home use (not vehicle vibrations) and tended to be 48 VDC based, which adds another complexity. 4 big batteries and a big inverter would start to make a serious dent in the amount of load I can carry in a 1500, which seems to be the only awd option.

    The high power after market alternators were kind of exciting price wise, although they do offer pretty impressive low rpm output performance.

    Even if I didn't run very long (1 hour) in battery mode, it would be handy to be able to run the a/c from a 110 V plug in setup, as many times that would be the case. This seems slightly more realistic at least power wise.

    I still need to study just how the factory optional rear A/C and heat units are setup on these vans as well. Some basic items I need to study:
    - I assume that both front and rear run from a single A/C compressor
    - Vehicle probably needs to be turned "on" in order to activate the temperature controls system, which might turn on other power draws
    - Regardless of a/c or not, just using it as an office will pull some power - at least 100 - 200 watts
    - Do some more reading about the significance of the standard vs heavy duty transmission option
    - See if a second alternator could be pushed into the normal a / c compressor location and move the compressor somewhere else.

    If I read the description correctly, the duramax diesel engine option includes a fairly large alternator and a second battery. I have no diesel engine experience, other than reading forums, so that might help. Most people I have met don't recommend idling a diesel very long though or they will coke up, so I am making the assumption that GM diesels are not immune to this either.

    edit - I don't see the combination of diesel engine and awd on either the chev or gm site, so maybe that combo does not fit / work.

    I suppose this is why R/Vs have generators to run the accessories.

    ---------- Post added at 05:30 AM ---------- Previous post was at 04:54 AM ----------

    Possible after market alternator.
    Last edited by harryn; 11-01-2010 at 07:32 AM.

  5. #5


    Hi, during the past 3 weeks I test drove 2 of these rigs.
    - Both were cargo versions, 1500s
    - The chevy one had the 6 cyl engine (4.3 L I think) and about 40K miles, RWD, 2008, side barn doors
    - The GMC version had the 5.3 l engine, new 2010, side sliding doors
    - I don't know the ratio setup of either, - should have, but didn't get this.

    A couple of interesting observations from these limited initial learning drive experiences:
    - The 4.3 L did surprisingly well, empy, on flat ground. No idea how it would do with some load or under hill climbing
    - It seemed quieter, but maybe the road was better (different dealer)
    - I didn't think I would like the side swing doors, due to them being narrow, but they were actually ok
    - The sales guy didn't seem to have any idea how to order a van or configure a new buy for future delivery. Maybe they have a specialist for this.
    - He said something that I thought was interesting - the rebate is based on "what is going when delivery is taken, not when it is ordered". Apparently, this has caused some customer consternation at time.
    - He could not locate a new AWD unit anywhere in his region (SF Bay area, CA, plus whatever reach he has.)
    - I am still just looking, but it was interesting to see this happen.

    GMC Version
    - The side slide door is big
    - Seemed noisy, and acceleration was not impressive, even with the 5.3 L on flat ground
    - The sales guy seemed somewhat more informed, even though he was newer.

    Both versions
    - If you are sitting in a parking lot, and you push down on the brake pedal, it slowly goes down to the floor. (all the way)
    - Is this normal ?



  6. #6

    Join Date
    Jun 2006
    River Ridge Louisiana-4 miles W of New Orleans-didn't flood-water stopped 800 yards away.


    I have thought about this very thing-and ended up just letting the motor run for 6 hours at a time.
    The V-8 uses about .7 gallons per hour at idle with the AC on-so about $2/hr for AC.

    We drive the 1998 Suburban to Flagstaff AZ(from New Orleans-3000 miles round trip) to stay at the La Quinta(allows dogs/pets) for 6 days in the summer when we have the $.
    Since we bought it-195,000 miles on it 3.5 years ago now has 215,000 miles--we have done the trip 3 times-6 overnight stops in Childress TX rest stop to sleep at the rest stops. I just let it idle with the AC on. I considered hauling a generator with a little window unit- but it just didn't make any sense or $$ and cents.
    Granted it seems wasteful to use a 250 hp motor to drive a 2-3 hp AC, but....
    Didn't seem to bother the motor- used good oil- Mobil 1 5w30 and 10w30

    A small window unit with a little generator mounted on a hitch carrier is the cheapest simplest way- other than just idling your motor.
    PS I considered "cold blankets" huge ice chest filled with ice, all sorts of not too practical stuff. GM has already done it the "simplest" way, but you might find a more efficient way. It kills me to waste the gas-a generator would use maybe .2 gallons per hour vs my 5.7 using .7 gph
    1998 suburban-
    1/2 ton

    199500 miles

  7. #7


    Thanks for the ideas. If I were just going to need a/c occasionally, running the engine overnight would be acceptable. Since this is going to be a portable office, the majority of the time, it will actually have 110V AC available, so it makes sense to try to use it rather than running the engine when possible.

    I need this to look a bit more professional, so a window a/c unit running from a generator is not going to happen. I suspect that the answer lies in the r/v options market, probably a roof mount unit.

    I did find this outfit ( redot ) that makes 12 volt DC based roof a/c units. So far, all I have done is look at the web site. My only real concern is that they units might be "too powerful" for the application, but I guess there are bigger problems in life.

    Anyone have prior experience with them ?
    Last edited by harryn; 11-11-2010 at 03:03 PM.

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