I am rebuilding a 1975 115 model 300D. Having sat for 6 years I am sure the AC system is empty. I thought that now would be a good time to convert it to R-134. I would like to keep it an R-12 system because everyone I know that has converted to R-134 complains that the new system doesn't cool as well as the R-12. But, by the same token, I was not interested in paying God knows what for the R-12.

I spoke with a German MB mechanic in San Antonio about this conversion and he assured me that I had to replace the York piston compressor with a rotary one. No mention made of the condensor or any other equipment replacement other than the dryer.

Today I spoke with the head man at the local auto AC supply house in Corpus Christi and he said that the York compressor was acutally better than many of the rotary comp. on the market today and that it was absolutely able to handle the R-134.

Secondly, he said that the main reason that conversions don't cool as well is that the old copper condensors are retained. He said that these cond. are not designed for R-134 and will not cool as well as the newer aluminum ones.

Newer cond. have many more, and smaller tubes, and they have tubes on either side rather that using one continous tube. He also said that when you change the cond. be sure that you get the biggest one that will fit in front of the radiator and that you seal the area between the cond. and the rad. so that there are no outside air leaks, i.e., all air that goes to the rad. must go through the cond.

He mentioned an R12 substitute called Freeze 12. It is considerably cheaper that R12 and can be used in R12 systems. He does not handle Freeze 12 because he feels that it is better to convert the system, but he says that he has not heard any negative feed back on it.

I would be interested in hearing any comments of R12/134 conversions.

I would suggest sticking with the r-12. You will be better off in the end. Think of the expense and the technical hoops you are jumping through to save $70-80 worth of refrigerant. How much is the compressor? Condensor? Hoses? Seals? You need a full flush to do it right...

Also, expansion valve and dryer (which you probably need anyways even for r-12).

Those '70s MBs did not have the greatest A/C capacity as it was. Stick with the r-12 to get the most out of it.

'Alternative' refrigerants are an even worse idea.

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1986 300E 5-Speed 240k mi.

csnow,

You are probably right about the costs. etc. Even though I live in S. Texas I don't usually use the ac, but woe be unto me if my wife has to use the car and the ac doesn't work. She is from N. Calif. and on a good day is not happy about living in this heat and humidity.

the amount you'll pay to convert the system will far exceed what you'll have to pay for R12 to fill it up. The mercedes dealer here in NJ still has R12 that they use to fill up the systems and keep them full.

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Whether you think you can or cannot, Either way you're right!. by Henry Ford.

I regret my 134 conversion on the W126.

I swapped the R-12 in my old 230/8 for 134A and have no regrets, but I did the work with great trepidation because of all the stern warnings of disaster that confronted me. Many of those warning are now confronting you, too.

So, first the folklore...

Won't cool worth a damn: I have absolutely no concerns here, seems to be cold enough to store meat for a month, and a thermometer in the dash vent hovers around 34F when the days are hot. This is Montana, but it does get hot in the summer. Still, if you are in a hot humid place, then your results may be different.

Hoses will leak because 134A goes through them: Haven't found this to be true at all, and techs I have spoken with confirm that this was an initial concern but one that has not been supported by actual experience. Seems the old oil seals the pores of the hoses somewhat. Mine did leak at one end fitting on the compressor, so I cut the end and re-fitted the compression fitting and cured the leak. I also added a small amount of commercial AC system stop-leak as insurance, cost $4.

You'll have to change out...: the only things I changed were the dryer and compressor. The dryers are not compatible because the bag that holds the dessicant for r-12 will dissolve with r134a. Change the dryer to one with a green tag, which denotes the proper bag, which also can be used with r-12 if you chicken out and change back. The compressor was changed because I rebuilt it three times and it was time for a new one. Got a York clone and only regret not getting a genuine York, althought it works just fine. I did not flush the old oil, just made sure the new compressor was filled with ester oil which works with r-12 and 134a. Most of the old oil goes with the old compressor, but that which remains in the evaporator and condensor will eventually migrate to the lowest spot in the system, usually the condensor, where it sits without causing any apparent problems. Here's where I had a problem...my system has tapered copper washers that seal the fittings. These used to be common but new systems use O rings so they are now less common. I eventually got mine at NAPA, but they were special order. There are at least two sizes on our cars, one for the dryer and another for the condensor and compressor.

What else?...When you charge the new 134a it takes about 80% by weight of the original r12. This is true. Use a gauge set to monitor pressures for your vehicle, and use a vacuum pump to dry the system before charging and to check for leaks.

My system seems to work just fine and after two years has given no problems while cooling just fine. If all this seems way too simplified, bear in mind it reflects what is called the "simplified conversion" approach that is endorsed by USEPA. I was skeptical at the start, but after trying it I would not hesitate to do it again. Although, as some posts say, if you have access to r12 and don't mind the costs, keep it so the system can stay as originally designed. I chose to convert because I had no option but to pay $50-$80/pound for r12 plus installation costs of mega-bucks more. 134a is about $2 a can on sale at Wallyworld, so if it leaks a bit this year or next year, so what?

Anyway, that's what has worked for my old 114 sedan, maybe it will work for you. I'm sure there are many techs with different opinions and recommendations. Hope this helps and does not make your decision even more difficult.

230/8

Ditto on 230/8's post.

I constantly read post about staying with R-12 but I can say that I converted my '84 500 SEL and am very happy with it. I replaced the dryer and compressor (A6 compressor as used in many old GM cars.) The compressor was shot. I flushed the system very good, Put in the prescribed amount of Ester Oil, evacuated and charged with R134. When I carged the system, I didn't have a sticker on the radator support so I had to go by imformation I could find, which was very conflicting. Finally I put in 80% of the lower amount I found in the information. Then I set the RPM to 1500 and while checking the temperature in the center vent with the system on high blower and coldest temp I would put in 2 oz and wait for the temp to stabalize and each time the temp would drop several degrees. I stoped the first time the temp didn't go down. I was very carefull to watch the pressures to make sure every thing was ok. Now the system works as well if not better than a friends 420 which still has R12.
Its been 2 years and I haven't had any leaks, I didn't change any O-Rings except ones where the system was opened.(dryer, compressor, maybe one other for the perposes of flushing the system.) Now If I have a problem, I shouldn't have any problem finding R134.
The other thing, being in the auto repair buissness, I have been hearing about a lot of the R-12 sold is coming out of Mexico,etc and it has propane in it. It cools fine but I feel it could be a hazard. So if you elect to use R-12 make sure it is checked with a freon identifier before you put it in your system.
There are atleast 2 sides to every debate. I choose the R134 side, you choose your side.

PS I tried the Freeze 12 and couldn't get it to work at all in my car. The pressures looked just like R12 but it didn't cool at all.

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84 500 SEL (307,xxx miles)

If you need to replace those tapered copper sealing washers and end up at NAPA, look for the counter guy with the white hair. He'll probably be old enough to remember when they were common items and may recall where to find them in the parts book.

Happy hunting,

230/8

230/8,

You do not say where you are located. kip is in South Texas.

To begin with 134, in a climate that demands the most your a/c can deliver (I'm sure that anyone who has been there would agree that South Texas demands EVERYTHING your a/c can deliver) will NOT keep you cool without adding a much larger, higher capacity condensor. The cost of the condensor in and of itself would cost much more than a few pounds of R12.

Secondly, your car has a two cylinder York or Tecumseh compressors. I can tell you from personal experience that they will NOT hold up under the added pressure of 134 in your climate.

Third, using an alternative such as Freeze 12, Duracool or any number of other snake oil refrigerants is fraught with its own problems.

Snake oil refrigerants fall in one of two categories, flammable or blends. The flammable are illegal in 18 states including Texas for obvious reasons. Blends are not really a problem until you have a leak. In the case of a leak the components leak at different rates, requiring total system recharge to get the blend back in its proper proportions.

R12 is going down in cost now because the cars that require it are hitting the junk yards in record numbers. With decreasing demand cost decreases.

Good luck,

Yeah, I think results should be accompanied with locale. Montana results versus Texas results are like night and day. I don't think my W126 would ever see 34 degrees in the summer with a factory perfect R12 system.

Sorry I left out my location.
I am in the southern part of North Carolina where the temperature in the summer is in the 90's with the humidity in the 90'S. R134 works fine.

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84 500 SEL (307,xxx miles)

As opposed to South Texas, along the coast, in August commonly being over 110 with super high humidity. Huge difference. There aren't a lot of places in the US with more demanding a/c needs.

Have a great day,

Demanding on the AC, krap, try you poor body.

When I bought my car a couple of years back, it had already been converted to R134-A. I live in Dallas and I have no complaints about the AC's effect.

The one thing that I have noticed is that if I am at a stop sign, the climate control kicks up the AC fan speed. But a minute after I start moving and as the engine rpm picks up, the AC fan speed decreases. I'm sure that happens with an R-12 system too.

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1986 300E (3/2002) Rear ended and totaled (10/2009)
2000 Xterra (5/2000)
1992 400E (11/2009) -Sold
1986 300E (12/2009) - Sold
2004 E500 Wagon (6/2013) - Sold

kip,

Isn't that the truth? I'm 55 and grew up in the Texas heat, albeit not in a part of Texas as hot as yours. It gets tougher on this ol' bod with every passing year.

hs_300e,

You are very lucky, or maybe easy to please. Of all the MB's originally equipped with an R12 system, the 124 is clearly the worst candidate for upgrade. Do you know what was done during the upgrade?

If they beefed up the condensor at that time, this would account for the success.

Glad you're comfortable.

Everyone,

It is always possible to achieve good cooling with 134 in a converted system, but at what cost? With a 609 license which is extremely easy and cheap to obtain, R12 can be had for $15 or so a pound. Most systems will use 3 pounds or less. So, for $45 you can buy 3 pounds of r134a for $15 and that leaves you $30 for the other things you need for the conversion.

Even the simplest proper conversion involves flushing, changing recieiver/dryer and adding ester oil. Can you buy flushing agent , an r/d and ester oil for $30? I don't think so.

Now that the cost of R12 is on the down slide, converting an R12 system is just false economy.

Have a great day,