A/C discussion: A different kind of propane injection... - PeachParts Mercedes-Benz Forum

CoyoteStarfish · #1 06-28-2008, 05:58 PM

Crazy idea time.

Time to redo my A/C system, Florida's heat can be brutal.

-Has anyone thought of or used propane as a refrigerant in their MBZ Diesel?

-What are the potential gains or losses from this conversion?

-Can "off the shelf" propane be used?

-How does it hold up in comparison (cooling) to R134a? R12?

-What kind of oil must be used?

The potential for a runaway if there is a system dump is startling. When my 134a charge blew, it dumped right into my intake (oops) and gave me a bit of a scare. But only raised the idle to about 1,100RPM.

Discuss!

JimmyL · #2 06-28-2008, 06:13 PM

WhiskeyDan tried it and it didn't work. Wasn't cool and the pressures were very high from what I remember....

Brian Carlton · #3 06-28-2008, 06:32 PM

Firstly, let me preface my remarks by stating that the discussion of hydrocarbon refrigerants on this board will usually cause one or more members to have a myocardial infarction.

The reason for this is the fact that such refrigerants may not be legal to use in your state and are also flammable if the system is ruptured. If you understand these risks prior to beginning any discussion of hydrocarbon refrigerants, then we have no need for a bevy of other members to post again and again regarding these issues.

So, to answer your question:

Propane, by iteself, is not the best choice for a refrigerant due to problems with it at higher ambient temperatures. However, when combined with isobutane, the mix is usually very good up to about 95°F. You can get such a refrigerant if you do a search on "Duracool". Their site gives you everything you need to know about it.

However, I state again............it may not be legal to use it in your state, and it is flammable.

Personally, I'm going to give it a whirl when the system on the SD takes a dive...........which is going to be soon.

Matt L · #4 06-28-2008, 06:59 PM

Consider a parallel-flow condenser, Brian. You'll need to make new lines, but the performance will be worth it.

Are you planning to use mineral oil or a synthetic?

CoyoteStarfish · #5 06-28-2008, 07:11 PM

Quote:

Originally Posted by Brian Carlton

...may not be legal to use...
---------
However, I state again............it may not be legal to use it in your state...
---------
Personally, I'm going to give it a whirl when the system on the SD takes a dive...........which is going to be soon.

My kind of guy.

Hey now, many forms of biodiesel and oil burning aren't exactly legal either. But hey... WINK - NUDGE - COUGH.

I would much rather risk blowing a couple pounds of propane into the atmosphere (or more technically; descending to ground level and dissipating harmlessly) than tetrafluoroethane if I screw up. My real concern is my couple of pounds of propane trying to blow me into the atmosphere if I screw up.

vstech · #6 06-28-2008, 08:34 PM

just to be a pain...
all refrigerants are hydro carbons...
well I don't think ammonia is...
http://en.wikipedia.org/wiki/List_of_refrigerants
hmm there are a lot of simple florocarbons... but a LOT are hydrocarbons...
all 134 derivatives are certainly hydrocarbons...

methane this and methane that... let me state this... most of them will certainly burn, and I would MUCH rather burn propane than ANY of the chlorine containing chemicals... WHIEW that stuff stinks when it's burned!!!

vstech · #7 06-28-2008, 08:45 PM

Quote:

Originally Posted by CoyoteStarfish

My kind of guy.

Hey now, many forms of biodiesel and oil burning aren't exactly legal either. But hey... WINK - NUDGE - COUGH.

I would much rather risk blowing a couple pounds of propane into the atmosphere (or more technically; descending to ground level and dissipating harmlessly) than tetrafluoroethane if I screw up. My real concern is my couple of pounds of propane trying to blow me into the atmosphere if I screw up.

both are carbon green house gasses. the 134 is just as flammable as propane, but burns MUCH messier...

Cervan · #8 06-28-2008, 11:09 PM

It is illegal to replace HCFC/CFCs with hydrocarbons in the US in
all but a very few limited applications (e.g. oil refinery compresors).

R-12 -> 60/40 (weight) propane/isobutane
R-22 -> 100 propane
R-502 -> unsure.. but maybe propylene or blend of propane/proplyene or
about 90% propane, 10% CO2 or ethane.

BBQ grade propane is often "wet" and may not be 100% propane, but
may have some isobutane or butane, esp down south to keep the
pressure down. If no HCFCs or CFCs or HFCs are present, small moisture
like < 200 ppm will not cause problems (unless super low temp).. If
fluorocarbons are present, then you should be < 10ppm moisture to
prevent them breaking down to acids. Use a refrigerant moisture
indicator, and dryers. We have seen propane at around 30-50 ppm
moisture.

basically you must find pure propane and pure isobutane. Propane alone is too high of pressures, (resembling r22 pressures, way over r134 pressures) Isobutane lowers the pressures, with a 60/40 mix it will lower them to r-12 level.

300SD81 · #9 06-28-2008, 11:22 PM

Lots of good info here, http://www.aircondition.com/wwwboard/alternative/index.htm

I'm going to be doing this mod again when I get my new car (previously converted to R134a, owner tells me its not very cold and it may need a charge) The best mix seems to be around 60/40 propane/ISObutane. Isobutane can be sourced at Ronson Multi-Fill Butane Refills and the 1lb Coleman propane canisters are supposedly one of the best. Get/make a high-side gauge if your going to do blend, you don't want to blow the system. More propane makes things cooler, but watch your pressures and do it on a hot day. Fill the isobutane first, then the propane. HC charge is going to be 1/3 of the R12 charge by weight. A side-can tap can be used to fill the isobutane. I fabricated my own propane line with hose clamped to the tip of a blowtorch.

#10 06-29-2008, 12:54 AM

Propane would work great if not for the fire/runaway risk.

sethyboy85 · #11 06-29-2008, 01:41 AM

I thought under pressure 134a was flamable?

For a propane leak to catch fire would require it to not disipate so rapidly which if you did get in a accident I doubt it would leak slow enough and not disspate in the air and come across 1000F temp for auto ignition to occur. I have been around some propane leaks and even if you can smell it doesn't mean the air is going to blowup if you light something...

Shoot if you are worried about that, then don't run on diesel cause that might combust in a accident as well. "Diesel: Flash point > 144F
Autoignition temperature: 410F

http://www.propane101.com/aboutpropane.htm

You will find in this thread that it's been covered and some "replacement" products contain propane, I know it old.
http://www.peachparts.com/shopforum/showthread.php?t=35692&page=2

CoyoteStarfish · #12 06-29-2008, 02:19 AM

Liquid 134 is highly flammable. I learned this the hard way

Trying to temp shock a torch-heated bolt into cracking (or just breaking loose) using an upside down bottle of "Dust-Off!" Fun shi..stuff!

Cervan · #13 06-29-2008, 02:37 AM

Quote:

Originally Posted by sethyboy85

I thought under pressure 134a was flamable?

For a propane leak to catch fire would require it to not disipate so rapidly which if you did get in a accident I doubt it would leak slow enough and not disspate in the air and come across 1000F temp for auto ignition to occur. I have been around some propane leaks and even if you can smell it doesn't mean the air is going to blowup if you light something...

Shoot if you are worried about that, then don't run on diesel cause that might combust in a accident as well. "Diesel: Flash point > 144F
Autoignition temperature: 410F

http://www.propane101.com/aboutpropane.htm

You will find in this thread that it's been covered and some "replacement" products contain propane, I know it old.
http://www.peachparts.com/shopforum/showthread.php?t=35692&page=2

Know whats funny about that flash point? its only 30 degrees off from some of californias deserts o.o

WDBCB20 · #14 07-01-2008, 12:11 PM

Here's the recipe to mix your own, scroll down to close to the bottom: http://www.vettenet.org/acfaq.txt Probably less trouble to go with a pre-formulated product such as duracool to lessen margin of error. The optimal mix (arrived at through scientific studies) appears to be 79% propane to 21% isobutane. In any case directions must be followed meticulously.

Works much better than R134a (134 in our old R12 system cars is useless at idle and in traffic with ambient temps in high 80's and high humidity) and causes noticeably much less drag on your engine when the compressor kicks in.