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Thread: Lil Red - Duramax 6600/Allison Conversion/Swap & OBS/NBS Dash Conversion

  1. #61
    Join Date
    Oct 2001
    Granby, Missouri, USA


    Thanks for all the info, Jim! I, for one, would like to see the A/C condenser modification info.

    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

  2. #62
    Join Date
    Feb 2000

    Post Update: 6-12-2024 - A/C Condenser Details - Got to be Cool!

    Lil Red had been on the road and drive-able for about 12 months by the time the following photos were taken. This means I had driven it through the previous summer (and The 2004 Diesel Page Rendezvous) without air conditioning. It was seriously hot that summer, and I knew that Lil Red simply had to have air conditioning going forward! One summer was enough to tell me I didn't want a repeat.

    By the time the truck became drive-able the year before, I had a pretty good idea how I would complete the A/C installation - I just needed to move through the process of modification/installation. And, I could lean on a friend and automotive A/C expert from Tampa, Florida (Gordon Marks) who answered all of my questions and even loaned me some of his hose making tools and supplies during this process.

    The above image shows the newly modified hood latch bracket, made to accommodate the added space required by the intercooler and A/C condenser. It was all TIG welded together. Most of the individual metal pieces used here for the hood latch bracket mod/extension were made from rectangular steel tubing.

    The long section of rectangular steel tubing was notched to allow it to extend 3-4" up the back side of the hood latch portion - to provide additional structural rigidity. The bottom of the new hood latch bracket (that bolts to the bottom of the radiator core support) includes a flat steel pad large enough (about 3" wide x 3" tall x 1/8" thick) to clamp the bottom part of intercooler to the radiator core support when bolted on. The upper portion of the modified hood latch bracket is likewise used to clamp the top of the intercooler against the top of the radiator core support. A 1/8" thick rubber strip was used wherever the modified hood latch bracket assembly made contact with the intercooler.

    Note: Moving the long section of the hood latch bracket a couple of inches farther forward meant the lower/center attachment mount for the grille will also need to be shortened by the same amount. In Lil Red I simply measured how much to remove, cut the plastic grille mount by that amount, then pop-riveted a 1/16" thick aluminum 90-degree angle onto the shortened plastic grille mount to accommodate the new dimension. Then, I drilled a new hole into the rectangular steel tubing on the modified hood latch assembly (with nylon insert, like OEM) to attach the shortened grille mount. Easy...
    --------I'm not using an air/ATF cooler - just the cooler inside the radiator. This lightweight truck doesn't need the additional cooling... plus the Allison has a deep-finned pan. On a hot day, the Allison runs at engine temperature around town, but drops some on the highway. If your truck will be used to tow, I'd install a factory ATF cooler in the upper area just to the right of (passenger side of) the hood latch mechanism. There should be enough room there. You'll have to fab some bracketry, but that should be easy for you at this point. Or... you could put a different shaped aftermarket ATF cooler in the area behind the holes in the bumper... Likewise with the smaller power steering cooler.

    I bought a brand new factory GM A/C condenser for this project - made for the model year of Lil Red, then modified it to fit. It wasn't that expensive... surprised me.

    Incidentally... The new condenser arrived without any paint on it... just raw aluminum. I initially wanted to spray on a nice layer of satin black paint, but in the end I just dusted on a thin layer to make it less visible through the grille. Paint can act as a thermal barrier, and I didn't want to hamper the condenser's ability to reject heat. So, if the paint looks a little thin here, that's why. The steel brackets, on the other hand were removed and properly painted before final assembly. I also used thread locker on the sheet metal screws used to fasten the new brackets to the ends of the condenser.

    The 3-axis position of the actual hood latch components couldn't be changed (hood latch, safety catch). The intercooler installation forced the condenser location to be father forward than the original had been. Mounting the condenser farther forward meant the condenser couldn't be as tall as the original. Shortening the condenser required removing the top 4 aluminum cross tubes along with the cooling fins that covered them. What's described here is the best way I discovered to modify the A/C condenser.

    Once I knew how I was going to mount the condenser and knew what mods were necessary, I used a 1/16" thick 4" diameter cut-off wheel on an angle grinder to carefully slice through the delicate fins just beneath the 4th cross tube. This worked well, but go slow, the aluminum cross tubes are thin walled and easily damaged. The remaining stub ends of the cross tubes on the far right side (passenger side) of the condenser were left long enough to allow the stub ends to be rolled over and crimped, followed by aluminum solder/welding. The stub ends that you need to solder/weld closed should be left long enough to account for a flub or two (i.e. the need to re-cut square, fold over, crimp and re-weld). The tubing is pretty thin-walled and delicate. I used a propane torch for this, and I practiced for quite a while on the excess tubing that had been removed earlier. You can buy the torch and flux-core aluminum welding rod at Harbor Freight.

    Removing most of the top 4 cross tubes and their fins to allow the condenser to fit, and then soldering/welding the ends of the tubes closed was the most tedious part of this. Honestly, I didn't know if this sort of modification would work when I began the condenser installation. But, in the end I didn't mess up the new condenser, and it installed nicely. Practicing your aluminum soldering/welding on the leftover condenser tubing you removed is essential... dare I say required. It took me a while to learn how to do it without melting the tubing.

    The above shows one of the bottom corners of the condenser, and how I made a bracket mount. The bracket is made from 1/16" x 1" wide steel strips bought from a local Ace Hardware store. The mounting bolt hole I used here, at the bottom of the new bracket (sorta behind the wiring loom), was one of the mounting locations for the original condenser. The right/left sides of the new condenser are mounted tight up against the intercooler, so I used a layer of dense double-sided foam tape to separate and cushion the sides of the condenser where each rested against the intercooler. You can sorta see the white strips talked about in these photos. The dense double-sided foam tape I used came from a friend of who owns a local auto body shop - though I only peeled the backing off one side (didn't want it to stick to the intercooler). The tape is made to attach emblems and trim onto cars... I imagine this tape can be sourced through retail outlets that sell auto paint and body supplies.

    The upper mounts were constructed as shown above - similar to the bottom mounts. The top most mounting bolt (behind the yellow arrow) was one of the bolt hole mounting locations used by the truck's original A/C condenser. In fact, all four corners of the condenser used the original mounting bolt location.

    As mentioned earlier, the A/C system has worked very well since the initial installation/R-134a charge in 2005. It's not needed a recharge, a top off or any other service. In addition to installing a brand new condenser, I also installed a brand new accumulator that mounts onto the firewall, in part because I was converting the original refrigerant used in this truck from R12 to R-134a - I wanted make sure there wasn't any debris or non-compatible compressor oil left in the system. Even on +100 degree days, the system can easily maintain comfort inside the cab.

    Because I was adapting a new style A/C compressor to an earlier truck, I needed to make a couple of hose assemblies. This was accomplished by using some new hose lengths and appropriate fittings, assembled using an A/C hose crimping tool. All of these items can be acquired online for not a lot, and Youtube will show you how to use them. Not hard! Contact me via email if you need additional tips.

    In the end, the cool factor arrived just in time!
    Last edited by More Power; 06-26-2024 at 10:18. Reason: words...

  3. #63
    Join Date
    Feb 2000

    Thumbs up Update: July 9, 2024 - Best Duramax Swapped OBS Chevy K1500?

    Added a new video today that asks the question... Also included is some basic performance discussion.

    You can help! Please subscribe to our Youtube channel - run your mouse cursor over the little circle truck image in the upper left of the video shown here.

    I recommend that you create a YouTube account. It's easy and free to register at, plus you'll be eligible for free stuff here in The Diesel Page very soon. By the end of July 2024 we'll begin offering all member-only online content here at TDP free of charge to those who are subscribed to our YouTube channel. Your YouTube account name will be linked to the free access list.

    TDP's long-term goal is to produce more free content videos, some derived from the several books we offer. The first book to be transformed into a video will be the "Duramax Service Guide". This book is, in my opinion, the most valuable book we offer. We're very close to the first in a series of videos about Duramax injector replacement and head gasket replacement, using the same sort of format used here in this video.

    The 6.5L Diesel won't be left out. More about the 6.5L Turbo Diesel Blazer as well as segments from the 6.5L books will be featured in video format as often as schedules allow.

    Subscribing will ensure you don't miss any new videos. As always, your input, suggestions and advice are all important.

    Last edited by More Power; 07-15-2024 at 12:23.

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