A/C parts year-to-year interchangeability

[euromobile900]

Another question, because I'm contemplating fixing my air conditioning while I'm mucking about with my electrics:
I see, on eEuroparts and the Saabsite, that different years of c900 had different years of air conditioning parts. For example, they changed the compressor three times, the hoses once, and the condenser and evaporator never. I want to know what the differences are. Can I mix and match and create an A/C system from many different years' parts? I see that most things were not changed the same year, so that indicates that the answer would be yes. The reason I ask is that some are much cheaper than others, and the Indie across the street has all three styles of compressor.

[euromobile900]

I'm also thinking about changing to propane for a refrigerant. I've been disgusted by the performance of my R134a-converted system, which lost the charge through a conversion fitting and never cooled the way I wanted it to. Preliminary research suggests that propane is more efficient than R134a, and with a flashpoint of over 1000ºF (a propane torch will not ignite on contact with red hot metal) I shouldn't have any troubles within the engine bay, and I'll likely smell it before any lethal concentrations occur if it leaks out of the evaporator.

[peva]

Yes Sam, I've heard of propane being used to great effect, but I've never tried it myself. Keep us posted.

[euromobile900]

The latest things I've read suggest that commercial grade propane is often "wet" with water vapor and may not be very pure. To fully mimic the exact characteristics of R12, you need a mix with butane, but I'm not sure about the percentages. However, one company (Duracool) sells A/C cans of a propane-butane mix. They're overpriced, but at least that way I'd know what I'm in for.

The idea, as it stands now, is to test out this stuff by charging the system with it and ester oil after a full flush with mineral spirits and compressor, receiver-dryer, and expansion valve replacement. If I need to switch (if performance sucks or something) I can always go straight to R134a because of charging the system with ester oil.

A fail-safe plan? I hope so. I've half a mind to abandon the hydrocarbon refrigerant idea altogether and just put in 134, at this point, because of how much other work I'm doing. But that seems like what everybody does. They go the safe route for the sake of not screwing up their hard work. And I want to experiment, because it seems nobody's really written this one up.

Advantages of the hydrocarbons are higher specific heat (something like twice that of R12) and lower operating pressures meaning less work for the compressor and thus less wear on it.

AS for the safety issue, I am confident, based on research papers I've read by the University of New South Wales engineering department, that it's unlikely it will blow up in my face.
link
Summary of the study: an explosion of a full charge of hydrocarbon refrigerant sent into a car's passenger compartment will not blow out the windows, nor will it kill anybody. Biggest threat would be the distraction to the driver and perhaps subsequent crash because of the shock.

Then, they went Mythbusters on us. The same engineering prof who authored the paper tested his theories by opening a can of hydrocarbon refrigerant inside the car and lighting a match...

Fast forward to 3:00 for the fireworks
To the author's credit, he did not suffer any effects from overpressure of the cabin, and the glass did not break. I just wish they'd done some stuff like turn on the electrics to prove that switch and relay arcs wouldn't cause an explosion. A c900, with its high rate of cabin airflow, is even less likely than that professor's tiny Ford to hold a sizable quantity of flammable gas for any amount of time.

[euromobile900]

Now I've nearly got all the parts for this A/C saga. And I've found out a great deal about refrigeration systems in the process.

It appears the Aussie engineering students and professors have done a great deal of experimentation with hydrocarbon refrigerants, because almost every google search I do leads me to their research. First off, the propane-butane percentage is 64% propane, 36% butane by mass (link). The Aussies (and Duracool, the purveyors of a propane-butane blend) also say to charge the refrigerant as a liquid instead of as a gas, as is done with R134A. Initially I thought this would be a good way to hydrolock-slug my compressor, but a bit of research shows there is good reason: when charging a blend of two different things, one usually evaporates at a higher rate, meaning the charge will not be homogeneous. Charging slowly (especially if you are using a long hose) means the liquid will have evaporated by the time it's gotten to the compressor anyway (link). Another weird thing Duracool suggests on their website is that a refrigerant should not be able to mix with its oil (suggesting that the refrigerant thins down the oil and causes it to lose its lubricity. This is a flat-out lie, because refrigerant is only going through the compressor in a gaseous state, so the oil has to come out of solution when the liquid evaporates, in the evaporator! The bottom line is that the compressor will be fed with oil mist, and if the oil does not mix with the refrigerant, it won't get carried around the system enough, eventually starving the compressor.

Having answered most of my questions, I bought a set of manifold gauges off Amazon, got a new receiver-drier and expansion valve (they come with the o-rings when ordered from Napa) and found an old compressor out behind the woodshed to use as a vacuum pump. I'll keep you all posted on how it goes!

[euromobile900]

Now I've nearly got all the parts for this A/C saga. And I've found out a great deal about refrigeration systems in the process.

It appears the Aussie engineering students and professors have done a great deal of experimentation with hydrocarbon refrigerants, because almost every google search I do leads me to their research. First off, the propane-butane percentage is 64% propane, 36% butane by mass (link). The Aussies (and Duracool, the purveyors of a propane-butane blend) also say to charge the refrigerant as a liquid instead of as a gas, as is done with R134A. Initially I thought this would be a good way to hydrolock-slug my compressor, but a bit of research shows there is good reason: when charging a blend of two different things, one usually evaporates at a higher rate, meaning the charge will not be homogeneous. Charging slowly (especially if you are using a long hose) means the liquid will have evaporated by the time it's gotten to the compressor anyway (link). Another weird thing Duracool suggests on their website is that a refrigerant should not be able to mix with its oil (suggesting that the refrigerant thins down the oil and causes it to lose its lubricity. This is a flat-out lie, because refrigerant is only going through the compressor in a gaseous state, so the oil has to come out of solution when the liquid evaporates, in the evaporator! The bottom line is that the compressor will be fed with oil mist, and if the oil does not mix with the refrigerant, it won't get carried around the system enough, eventually starving the compressor.

Having answered most of my questions, I bought a set of manifold gauges off Amazon, got a new receiver-drier and expansion valve (they come with the o-rings when ordered from Napa) and found an old compressor out behind the woodshed to use as a vacuum pump. I'll keep you all posted on how it goes!

[euromobile900]

Here's another article about A/C system filled with propane catching on fire. This brings the grand total of real life (not set on purpose) hydrocarbon refrigerant fires to 1.
(link)