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Charging dash A/C with hydrocarbons - alternate method [message #305055] Sun, 07 August 2016 10:16 Go to previous message
gladius is currently offline  gladius   United States
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For those of you who'd like to get the best possible performance out of your dash air conditioner, without using poisonous/patented/underperforming DuPont crap (R12/R134a), as you may know Duracool is an excellent drop-in option that many here have had much success with. It contains a mixture of propane and isobutane. At $9 for a 6oz can however, it's not exactly cheap. Here is alternate way of charging an A/C with propane/isobutane that would be more suitable for an experimenter and/or cheap SOB like me, particularly if charging multiple vehicles, as it's much cheaper per can and more versatile.

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Items needed:

MSR IsoPro camp fuel 8oz -- $6/can, bought from the local Academy Sports and Outdoors. This contains 80% isobutane and 20% propane.

Coleman propane camp fuel, 16oz -- $3/can, can be found anywhere and everywhere. With the right fittings you can refill these from a larger bulk tank for less than 50 cents per pound.

Coleman propane extension host -- $27, from Amazon

Lindal valve to throwaway propane canister adapter -- $31, from Amazon.

Yellow A/C charging hose -- I bought a full set of three hoses for $13 from Amazon.

A gauge set is helpful, but not required.

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You'll need to cut the yellow charging hose, cut the Coleman propane extension hose, and join the two together with brass fittings and hose clamps. The prices for everything have gone through the roof these days so expect to spend $15-20 for the fittings. I recommend installing a brass shut-off valve, especially if you don't have a gauge set. If your coach has been converted to R134a you should have quick disconnect fittings installed on the factory 1/4" SAE schrader valves. In this case you will need a female R134a quick disconnect adapter to connect your charging hose. I recommend getting the 90* fittings with a shutoff valve built in. Uxcell sells some nice ones on Amazon for about $13 each.

This guide assumes your A/C is already in basic working order; maybe low on charge, but with no major leaks or equipment failures. First start by evacuating the existing charge. I recommend venting the toxic DuPont crap into the atmosphere so it will never again have the opportunity to contaminate someone's A/C system. Otherwise if you feel it necessary for some reason, take it to an A/C shop and have them recover it.

You will need to decide what ratio of propane/isobutane you want to run, and calculate the charge amount accordingly. It's said that 60/40 propane/isobutane is the optimum ratio for drop-in R12/R134a replacement. This makes things simple, as if you charge the MSR IsoPro and Coleman propane in equal amounts, it will result in a 60/40 ratio. If the ratio is slightly off it doesn't matter. You can also experiment with different ratios depending on your desires, operating conditions, etc. People in extreme conditions and those wishing for better fuel economy/less compressor drag may want to run more isobutane; for better cooling per pound in normal climates use more propane. You can go as low as 20/80 propane/isobutane (using MSR IsoPro cans only; no Coleman fuel) or up to 75/25. The more propane you run, the higher system pressures will be, and the more load there will be on the compressor when it kicks in.

When the system is empty, you can begin charging. It's pretty simple. Just charge it the same way you would any other refrigerant, except using your new spliced together charging hose. Be sure to bleed all air out of the hose(s) before charging. The early coaches use 3.5 pounds (56 oz) of R12, and the late ones (77-78 I think) use 3.75 (60 oz.) For optimum charge with hydrocarbons, use only 36% of the R12 total. That's 20.2 oz on early coaches, 21.6 on late models. The amount charged does not have to be exact; you can go an ounce or two over without hurting anything. Remember, if a 60/40 ratio is desired, use equal amounts from the MSR IsoPro and Coleman propane. If other ratios are desired you will have to do some calculations to figure out the right amount to charge. Start your charging with the IsoPro first!! This way system pressures will start out low, and then will gradually increase as you charge in the propane. I recommend charging as a liquid by holding the can upside down, but be very careful to crack the valve open slowly and take your time with it so as not to accidentally slug the compressor by flooding it with liquid.

When you've finished charging, you will have COLD A/C! My coach on a 95-100+ degree day has no problem icing up the evaporator with the cycling switch shorted to run the compressor constantly. It will easily blow 35* temps out of the vents like this, but of course, this isn't sustainable as the evaporator will completely ice over. With the compressor cycling normally, vent temps will hit 43-44* with the evaporator alternately icing and thawing. That's the best you're going to get out of a stock GMC with its terribly restrictive heater/AC box and vent design, with no insulation. There is much more refrigeration capacity than is actually able to be used due to this poor design. It's good enough however; at idle and driving down the road the A/C works great and feels comfortable even with no privacy curtain installed to keep the cold air up front.

On a final note, some people make a big deal about the impurities present in camp fuel. It's true that camp fuel is not refined to the same degree as the base stock Duracool and other companies use. All propane sold in the USA is rated HD-5 which means it's at least 95% propane, with the majority of the rest being other hydrocarbon gases which are also themselves refrigerants and will not cause any problems. There may be a tiny bit of non-condensible gases in there, which isn't enough to harm anything, and won't be pulled into the system if you charge as a liquid. There is also likely to be a tiny bit of water vapor present, but again, this is harmless; your desiccant will absorb it quickly.

What I love most about doing things this way is that the refrigerant is CHEAP. It costs a bit of money to buy the necessary adapters and fittings, but I don't care as I love to acquire new tools that expand my capabilities. Having bought the necessary tools, the total refrigerant cost to fill up a GMC is $15, or about $10 not counting the refrigerant that's left over to be used on other vehicles. At these prices I can afford to stockpile a large quantity of refrigerant to fill all of my vehicles and others' too for decades to come. With the right fittings for my bulk tank I can also refill the propane cans for less than 50 cents each, which makes the propane cost practically nothing. This is especially useful for charging R22 systems, which can be done basically for free. Kiss my ass DuPont!

That pretty much covers it, but feel free to ask any questions you may have.

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