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ReGassing AC system with Hydro Carbons (LPG)


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8 replies to this topic

#1 el_freddo

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Posted 29 December 2012 - 07:07 AM

G'day,

I'm super keen to get my AC back online - I've never had it all hooked up since buying the car many years ago. It's all still there but now with an EJ compressor. I'm hoping to have a set of custom hoses made up to adapt this AC pump to the EA system.

I'm after information as to how to go about refilling the system - what oil and how much to use and where to get the dye from too. Then how to add it all in and how to vent air in the process.

Also does anyone know what PSI the system should have in it?

Cheers

Bennie

#2 mdcc2010

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Posted 29 December 2012 - 04:14 PM

Hydrocarbons are generally frowned upon in automotive refrigerant systems, regardless of how little there is in the system and how safe it may or may not be. I personally don't want to use them, mostly because of any potential legal aspects that may present themselves if it were sold or ever in an accident (or somebody ratted me out to my insurer/any relevant authorities).

If your system was originally R12, you've got mineral oil in the lines, while an EJ compressor made post-'94 will likely have PAG for using R134a, and these oils are incompatible with one another. Bottom line: you'll have to flush your lines/condenser/evaporator and drain your compressor and use Ester oil instead (compatible with R12 and R134a and their residues). You'll install any dye at the same time, usually in place of .5 oz of oil.

If you've got the money, I suggest replacing your condenser and using R134a: if you swap your tube-and-fin R12 condenser with a parallel flow condenser made for R134a, there will be no reason to use any alternative refrigerants since you'll have effective heat rejection with the new condenser, and it will keep you from having to deal with any issues down the line stemming from the use of blends or HCs.

Air venting is done using a vacuum pump that is capable of pulling down -30 inHg; any level less than that will not work to flash moisture from the system (moisture in the system is very bad, fyi). Basically you'll connect the vacuum pump to a sealed system, run the pump for about 15 minutes after the gauge reads -30 inHg, close the vacuum line and shut down the pump, and then let it sit for about an hour. After the hour is up, check the gauge to make sure it still reads -30 inHg; any drop means you have a leak to fix. If the gauge holds, then the vacuum pump is removed and the chosen refrigerant is introduced; there's no need (or indeed, any possible way) to remove air following a successful vacuum operation and a proper system charge short of a complete recovery and recharge operation.

If you must use an alternative refrigerant, there was talk made of using the contents of certain varieties of canned air as refrigerant (there are several threads on rx7club.com and elsewhere), and it's cheaper, safer, and more ozone-friendly than R12, R134a, and hydrocarbons, and also more effective in a retrofitted R12 system than is R134a (when using a tube-and-fin condenser).

As far as the amount of oil and refrigerant to use, there ought to be a sticker under the hood that specifies how much of each, or you could search for info for your compressor model since it's not the one that came with your car. Typically the refrigerant quantity is listed as weight in ounces, not pressure. There exist many charts for converting the proper charge of R12 into anything else (example: 21 oz of R12 = 19 oz of R134a (10% less)).

As for the pressure gauges, they're mostly there as a diagnostic: they show you when you've established a proper vacuum, and the readings they display when the system is running are useful in pinpointing failures; charging is typically done by precisely administering the specified quantity of refrigerant, not by reading gauges. That being said, if you don't know exactly how much refrigerant you'll need, you'll have to use the gauges and ballpark it, either administering more or venting off excess depending on how your gauges read. Low-side pressures usually read between 25 and 35 PSI for an average system's full charge, but the high side varies greatly: for the pressures you'll need to shoot for, that depends primarily on your chosen refrigerant; all refrigerants have different operational pressures, and you'll have to search for the data once you decide what to use to charge your system.

#3 El Presidente

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Posted 29 December 2012 - 09:41 PM

Do you know what refrigerant your EJ compressor originally came with? My thought is that if Australia is one of many countries where R12 is still used and available, both your EA and EJ A/C stuff might be compatible already.

If you can, stick with R12, it works the best. Several Jeep guys run propane or butane and from what I've heard on the forums over there, is that it does work fairly well. The amount required is so minimal that its safety is kinda a mute point and I'd be far more concerned with my fuel lines breaking. Alot of the R134a refills you'd find at the parts store are actually blends of different refrigerants and propane and butane are two of the common ones used and it seems safe there. Filling your system with propane/butane is guess work for a shade tree mechanic, but its been done before on several makes/models of cars so I bet a little time on Google could dig up some good info.

Don't bother with R134a, its not as efficient as R12, is hard on R12 systems and last I heard is being phased out in 2016 here in the US, so no refills will be available for us.

Josh

#4 Leeroy

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Posted 29 December 2012 - 11:06 PM

HyChill's Australian website lists the capacity needed for HyChill Minus 30 (also known as HR12)

http://www.hychill.com.au/products/ Under the heading Automotive Weight Charts...

#5 presslab

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Posted 31 December 2012 - 01:07 PM

I use ES-12a which is a mix of propane and isobutane meant to have similar vapor pressures to R12. I imagine you can get something similar over there. Hydrocarbon refrigerants are compatible with any oil, unlike R134a. So if you want to flush your system and replace the oil, I'd recommend double-end-capped PAG, which is shown to be the best lubricant, or POE which is compatible with both R12 and R134a.

The pressure switches and condenser are designed for R12 on my '88, so I didn't want to "convert" to R134a. The ES-12a works great! They specify to not charge into a "hard vacuum"; in reality what that means is you should add a bit of air into the system, it's been shown that this improves things a bit with the hydrocarbon refrigerants.

1) Vacuum it down for an hour to boil out the moisture, and then let it suck a bit of air back in until the vacuum is gone. Point a large shop fan at the radiator/condenser if you have one.
2) Charge with liquid (can inverted) with the compressor off, and let it sit for a few minutes to allow the refrigerant to evaporate.
3) Start the engine and block the throttle for a fast idle about 1500 RPM. Engage compressor and then SLOWLY charge with liquid. Don't add it too fast or you can damage the compressor.
4) Keep adding refrigerant until the high side pressure is about twice that of the ambient temperature in Fahrenheit, plus 20 PSI. For instance, on a 90-degree Fahrenheit day, twice 90 is 180, plus 20 equals 200 PSI. Low side should be less than 35 PSI.

#6 el_freddo

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Posted 02 January 2013 - 08:41 AM

Thanks for the info guys!

R12 has been banned for sale in Australia for some time. From what I understand if an authorised operator still has it in stock (re-claimed) they are allowed to use it on a well serviced system. But they are not allowed to buy more fresh gas.

I'm keen for this hydro-carbon setup. Sounds like I can use my current system without any changes and it's better for the environment if the system leaks at some point.

I've got some research to do now. The only question I've got at this point is where can I get a vacuum pump from?

Cheers

Bennie

#7 grossgary

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Posted 02 January 2013 - 08:58 AM

might be able to rent one from a tool rental company.
shops here will pull a vacuum only for you.

you can also buy cheap ones. really cheap:
http://www.harborfre...tors-96677.html

more expensive:
http://www.harborfre...pump-66466.html

Might not be perfect but Subaru A/C systems are very robust and not prone to moisture related issues, I've never actually seen it happen even on old 1980's stuff. A sealed Subaru A/C system generally lasts the life of the vehicle without issues and there's dessicant in the drier that will take care of residual humidity. I do tons of A/C work and the vacuum pulling, is way overkill and uneccessary if someone wants to skip it. This will be unpopular but I have all but quit pulling a vacuum, until I see one failure I'm not giving up the practice. So far the time/money/effort saved has been well worth it. I understand all the theory and mechanisms involved, but practicality trumps technical arm chair banter for me.

#8 presslab

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Posted 02 January 2013 - 11:05 AM

I use this vacuum pump. The CFM doesn't matter on a car system, but the two stages allow it to suck a tighter vacuum. Maybe you can find a two stage pump like this.
http://www.amazon.co.../dp/B000O1E5UQ/

I opted to flush my A/C system and it's a good thing I did. The green corrosion slime inside was gross. That's probably why my compressor was on it's way out with a rattling; when I did my engine conversion I used the EJ compressor. Has your A/C system been left open for any length of time? If so I'd recommend flushing the system and at the least replacing the dryer. You can also reactivate the dessicant in the dryer using your baking oven, but the Mrs might not like that. :Flame:

I used a '98 Legacy compressor, and I found an Impreza suction line that fit perfectly in my '88 wagon, attached at both ends just fine. On the discharge line I TIG welded the old pipe to the EJ pipe. I kept a wet rag near the rubber hose part and it didn't get damaged.

#9 suprunner

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Posted 01 April 2013 - 06:07 PM

.....
Might not be perfect but Subaru A/C systems are very robust and not prone to moisture related issues, I've never actually seen it happen even on old 1980's stuff. A sealed Subaru A/C system generally lasts the life of the vehicle without issues and there's dessicant in the drier that will take care of residual humidity. I do tons of A/C work and the vacuum pulling, is way overkill and uneccessary if someone wants to skip it. This will be unpopular but I have all but quit pulling a vacuum, until I see one failure I'm not giving up the practice. So far the time/money/effort saved has been well worth it. I understand all the theory and mechanisms involved, but practicality trumps technical arm chair banter for me.

 

I just did an EJ swap, and I got custom hoses made for my a/c system. From what you are saying, I can just get a can of 134a and throw it in? No vacuum needed?

 

Thanks,

 

Greg






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