I hope your wife does most of the shopping for your family. Maybe she is more dilligent in finding the bargains.

I agree that R12 itself is more expen$ive than 134. Everyone knows that although many people are suckered into believing that it is more expensive than it really is. That said, you need to look at the big picture. What kind of siense does it make to spend a bunch of money on other items so that you can save a little bit of money on the refrigerant itself? Once converted, in almost all cases, you CONTINUE to spend more money due to the decision to downgrade the system.

Even in this thread after pointing out the downside to a converted system, there is talk about spending big bucks for components so that they can save a few bucks on refrigerant.

I'm a really old guy and learned my mathematics in the fifties and sixties before the introduction of what they at the time called "new math," so maybe my mathematics is just different from the younger folks.

Also, I have a bad habit of rapidly perusing threads. I was under the impression that the original poster was replacing the compressor, thus would be flushing and recharging the system anyway. One of the recent posts points out that he is not emptying the system, so if that's correct I got the wrong impression of the original situation. That said, if I were to buy the car, I would reverse convert to prevent the problems that will almost assuredly develop within the next few years. I have reverse converted quite a few systems and it's not that big of a deal and provides a really good insurance policy against future major problems. The fact that it gives me back the additional 15% cooling capacity is also important in Texas.

I think it's more of a language problem: failing to recognize the correct answer when told!!!

All Arguments aside... Simply put, my fittings are 134, that's what I'm sticking with. While both refrigerants have their ups and downs I was looking for helpful tips into working on the AC system, I've never working on a mercedes one and I wanted to find out what I should be aware of before getting neck deep into it.

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

Ok, here's a tip. Since your original compressor locked up, you should assume that it has spewed debris into the system, because it almost surely has.

Most the debris will go toward the condenser and dryer, but enough of it will also shoot into the evaporator as the pressures equalize when the compressor fails.

You need to plan on a complete system flush, or you'll likely be replacing that new compressor again in short order.

In my opinion, the biggest problem with retrofits is that you must use an oil which tolerates chlorine, as chlorine will be present in the rubber parts of the system. That is, unless you replace all of the hoses - perhaps yours were replaced, judging by the fittings.

PAG is the oil of choice for 134a, but you're forced to use POE or such in a retrofit.

A.E. ,

Grenaded Comp.or not(It don't matter,you're going to Clean/Flush/Replace almost all the A/C system components), the only way you'll be happy with
a "Retrofitted" 134 system in Florida (with your Originally R-12 System,which
has the "Designed For" LOWER Pressure Compressor) is to retrofit a Parallel
Flow Condenser.

T'were me:
1.New Nippondenso Compressor designed for 134
(the O.E. R-12 Comp. Never lasts long @ the Higher 134 Pressures.)
(Make sure you fit an inline filter)
2.New Parallel Flow Condenser.
[Yeah,I know ,You'll need custom condenser lines made up.]
3.If needed (AND unfortunately it will most likely be) New Evaporator.
4.Flush EVERYTHING else.
5.New RD (Last Thing)
6.BG Frigi-quiet for Lubricant.
7.Vacuum minimum 24 hrs (AFTER determining system "Leak Tight")
Fill with proper amount of 134

(You can NOW repaint the MB Black and retrofit BLACK leather interior and
still be Uber comfortable in Florida.)

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'84 300SD sold
124.128

Although my memory is admittedly very short, your situation was as I remembered, empty of any refrigerant and a failed compressor.

Regardless of the refrigerant you choose, if you want even a little life from your new compressor, you must break all connections and flush both ways, thoroughly blow out flushing agent with compressed air, replace all o-rings, lubricate them with Zylog, put new compressor in place, distribute 8 oz. of oil throughout the system and last thing install the new filter/drier and be ready to evacuate system as soon as possible after installation of dryer.

The reason my first post in the thread pointed out that this would be the ideal time to reverse convert is because the entire operation is exactly the same for a reverse convert as it is for a failed compressor replacement, minus the compressor issue itself, of course.

Being in Florida, you are missing a golden opportunity to make a serious improvement in the performance and longevity of your a/c system by staying with 134, but it is, of course, your choice. Regardless of refrigerant choice, don't even think about slapping in a new compressor without flushing the debris and oil out of the system. If you do, you will be working on it again soon.

Best of luck with it.

Not to add fuel to a fire, but is it true that the R12 is more efficient and will therefore affect fuel mileage to some degree? I've read this somewhere back in my aging memory, ... have always wondered if it is true and if so, significant.

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Gone to the dark side

- Jeff

wow, fuel mileage differences... hmm I'm sure there is a difference. the pressures will be higher with 134, and you'll be using it on max recirculate, with 134, where 12 would be so much better that it may cool sufficiently on normal, or even low, so I'd bet there is a noticeable MPG hit with 134.

*sigh* I'll kick myself for asking... but if I were to reconvert. how much 12 will I need, and the oil etc

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

There should be a sticker on the core support indicating the exact charge by weight. If it's not there, let me know and I will check the one on my 88 300E. It is probably the same. I think that the oil charge is 8 oz.

Due to lower high side pressure, I expect there to be a fuel mileage difference, but it is probably so small that it would be unmeasurable. I would not consider this a meaningful factor in a 12/134 decision.

I am not sure about the diesel models, but I know for a fact that the early 300E and the later E320, both 124 cars, had different condensors. If I'm not mistaken the later E320 has a parallel flow condensor. They are definitely two different part numbers because they look different.

The 124 cars are better candidates for 134 conversion than are the 123 cars, but that's not saying much. The 123 is probably the worst candidate for 134 conversion than any car I've ever had my hands on.

don't forget the 93 I have is an early 134 vehicle. 94 was the transition year for cars.
however, when I had the 95 300D, I thought about swapping parts over from it to have a larger condenser, but they were the same.
the 124 condenser is larger than the 123/126 condenser, and the coils are much smaller. so it's capacity for heat dispersion is greater. perhaps the 124 condenser was designed from the beginning for 134?

Not trying to hi jack some one elses repair thread but- My 86 300 sdl has r-12. The a-c has has a major wiring hack job(either by po or original owner.) I have had the AC kick on and work at highway speed. As far as i am concerned it does not work.

Where would i start?

I need the console pice that hold the swithes for climate control. I am guessing that would be first?

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86 300SDL. 250,xxx on #14 Head. One eye always on temp gauge.. Cruising towards 300K

first would be to chart what the system does.
I'd worry about cosmetics last. unless you are saying you don't have the switches themselves...

Yes I remember looking at a 93 300D back in the mid nineties and was surprised to see that it was originally 134. So I am not surprised that the 93 and 95 have the same condensor. I would expect the 124 diesels of the eighties to have different condensors form these later models, however, as did the gaa cars.

Are you sure that the later 124 cars do not have a parallel flow condensor? For those that are forced into using 134 in their early 124 cars, a PF condensor would be a great improvement.