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Old 05-07-18, 12:38 AM   #1
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Default Converting vehicle A/C from R134A to propane?

I have a 1998 Jeep and the air conditioning has a very slow leak. It's not a big deal, I only have to top it off about every 6 months. With that said, I'm interested in converting it to use propane refrigerant instead of R134A. I know that propane works at lower pressures and is more efficient/colder than R134A, and is a common replacement in older vehicles that came from the factory with R12. I strongly dislike R134A due to it's higher pressures and rather poor performance. Propane is also cheaper to keep topping off.

I've been searching google on this topic and I can't find a lot of information regarding converting R134A vehicles, it's all about older R12 systems. (probably just because you can't get R12 anymore)

I'm wondering if it would be OK to convert the 134A system to propane without any modifications? Would the thermal expansion valve still operate in an acceptable range? Would there be any problems with compatibility of the oil in the system, or the compressor itself?

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Old 05-07-18, 09:23 PM   #2
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R290 operates at higher pressures. You want some mix of R290 and R600a. Or just use R152a, commonly found as duster cans.
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Old 05-10-18, 12:45 AM   #3
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Propane and butane mixture works well.
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Old 05-11-18, 09:27 PM   #4
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That's interesting...I thought 134A wasn't a very efficient refrigerant because it was higher pressure. Will a propane/butane mix provide better cooling? Can I simply vacuum and charge the system with it, without making any other changes?
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Old 05-12-18, 08:18 AM   #5
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I think the hydrocarbon replacement for R-12 is called freeze12.
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Old 05-12-18, 08:00 PM   #6
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Quote:
Originally Posted by oil pan 4 View Post
I think the hydrocarbon replacement for R-12 is called freeze12.
I'm not asking anything about R12.
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Old 05-12-18, 11:13 PM   #7
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I really think R152a would be your best bet. No need to get the mixture right, just put a can tap on a duster can and put it in the low side until the subcooling is what you expect.
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Old 05-13-18, 09:21 AM   #8
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The aftermarket natural refrigerant blends are a precision blend of propane and isobutane. Isobutane has a boiling point of around -10 degC where natural butane has a boiling point around 0 degC at sea level. Propane has a boiling point around -40 degC. What this means for the conversation here is that both types of butane do not develop enough vapor pressure compared to r134a, and propane develops too much vapor pressure. The care line of refrigerant is either a blend or pure propane isobutane. Care 30 is closest to r12 or 134 and is about half and half of each.
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Old 05-13-18, 10:14 AM   #9
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R134a is the replacement for R-12.
A product called freeze12 is a propane blend drop in replacement for R12, it should also work for replacement of R-134a.

Jeff explained how we need R-12, R-134a and propane blends to achieve certain pressures as they phase change.

Straight propane would be more like trying to replace R-22 or R-410a. If either one of these were used in an automotive A/C it would break something because the pressures would be way too high.
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Old 05-13-18, 10:22 AM   #10
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Here's some info on r152a. It was recommended by the EPA over r134a during the r12 phase out process. As a drop in replacement, you will lose a little capacity versus r134a. Maybe 10 percent.

Check out the graphs and this article:
https://www.kth.se/itm/inst/energite...del-1-1.686423

If you're looking for quick and simple, the r152a is a single substance. Since you have a leak, using a mixture is sketchy because the more volatile substance (propane in this case) will boil off first whenever it can. Also, since isobutane has a boiling point around freezing, when the mixture becomes mostly butane, you could end up sucking air into the low side if that's where the leak is. With decreasing mass in the loop comes decreasing suction pressure, so at a certain amount of leakage, the evaporator circuit will be operating well below atmosphere.

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