my AC compressor is leaking and now the system is 'flat' and will not even engage. I have an R12 system and was wondering if it is a good idea to convert to R134 given that I will need to get the compressor fixed. Also, is it worth doing a reseal on the compressor or buy a rebuilt one?

If you can keep the system on R12 then there is no need to convert to R134A. The system was originally designed for R12 and will yield better performance as opposed to R134A. Most people are not satisfied with the results of a conversion, even one that was done correctly. These cars just don't convert well.

As far as the compressor is concerned, you may be better off obtaining a quality rebuilt depending on how many miles your current one has logged. They do wear out eventually.

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1989 300CE

Statistically cars converted to 134, even a thorough conversion only last 2 years before serious attention is again required.

The cars requiring R12 are now quite old and hitting the wrecking yards or the crushers in record numbers. This has decreased the demand for R12 which of course has decreased the price. It is now available at prices not much higher than 134.

I have seen people spend literally $1,000 to convert to 134 so that they can save $50 or $60 on refrigerant. I guess I'm old enough that the math I learned was different from what has been taught in later years.

Stay with R12. Leave the 134 and worse yet, the junk refrigerant conversions alone.

So if you had a car that was converted to R134a, was working, but not quite as well as you would like would you back convert it to R12? How hard is it to get the R134a oil out of the evaporator? The compressor needs to be unmounted and cleaned out, right?

-Jason

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

I have reverse converted a number of systems with great success. The procedure is documented in numerous threads on this forum, but I will repeat it once again:

o If the system is not empty, recover the remaining 134.
o If there was a leak that led to service, repair the leak.
o Break all connections and flush all lines and components thoroughly preferably using a/c flushing agent, but Brake Cleaner or Mineral Spirits will get the job done. Blow the flushing agent through the line and then blow all of the flushing agent out of the line or component THOROUGHLY with compressed air.
o Remove the compressor and turn it by hand to empty as much oil as possible. DO NOT flush the compressor with flushing agent, use Mineral Oil for this purpose.
o Distribute the correct amount of Mineral Oil through the system by pouring a little in each component.
o Put the compressor back in place, turn it by hand at least a dozen turns to ensure that it is not liquid locked with oil.
o Lastly install a new r/d and don't do it until you are ready to immediately begin evacuation as soon as it is installed.
o Evacuate and charge the system with R12.

I went from R12 to R134a, as recommended by my (now obviously former) mechanic. There are two problems with the conversion:

1. R134a is not as strong as R12, i.e. it will not cool as well as R12 does.
2. R134a operates under higher pressure, meaning a tired compressor will fail more quickly, but worse, you will have a pretty much guaranteed expansion valve failure. Though the part is not expensive, shops charge an arm and a leg to do it. Also, tired hoses will fail more quickly.

I repaired the expansion valve myself, and replaced bad hoses. The compressor lasted three more seasons after the conversion before it became so weak that I swapped it out with a Denso rebuilt that was advertised as being R134a capable.

The A/C is working all right, but not as efficient. I have purchased a parallel condenser that supposedly would add about 10% or more efficiency into the system, but have not yet had the time to have fittings and hoses made to install it. For Washington D.C. thought, with the new compressor, new expansion valve, and so on, the conversion works adequately well.

For replacing the expansion valve, I did a writeup here. Shop wanted at at least $1,200 to do it, the part is about 40 bucks, and I did it in an afternoon, with the experienced help of my friend Chuck (a moderator of this board).

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

I don't get it! Why pay money for a parallel flow condensor and keeping going down this admittedly rough road? R12 is now in much less demand thus it costs only a little more than 134 these days. Reverse convert and solve your problems.

Nope - there I am not so free. Simple reason: wife! She is in EPA's upper management. So we are not touching R12....

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

What does her position have to do with legally using a refrigerant that was legally put in the car at the factory. Go online and take a test and get EPA 609 certification and buy the R12 LEGALLY. Does the EPA have a problem with you performing legal service on your vehicle using legally acquired goods and supplies?

You can take the test online in an hour or two at the most for a $15 fee.

I don't want to mess with it. Period. So I am keeping mine at 134a.

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

It's your money and your car. We are free in this country to do with our money and property as we see fit, at least to a point, and for now.

$1,200 is WAY too much money for changing the expansion valve. Since you are committed to following the EPA guidelines, I hope that you recovered the refrigerant when you did this job. If you vented it, that would be a violation.

As a reminder, to follow the Federal law, the system must have correct fittings and proper labeling. You must also use shutoffs in your gauge set no more than 12" from the port. This and further information is all in the 609 certification information. There are probably just as many or more violations of Federal law in converting and servcing converted systems than there are in handling R12. Since you are committed to following these laws, which is commendable, perusing the information online would be helpful for you.

Good luck with it.

Jeez maneeze! Just because I disagree with you on R12, you are laying it down hard.

I did not realize you had to evacuate the system after a blown expansion valve and a bad compressor hose. Wow!! I learn something new every day.

(think of the logic - of course the system was EMPTY! Blow expansion valves and bad compressor hoses lead to EMPTY SYSTEMS! But when I did do the compressor, I did have the R132 recovered professionally first. In fact, my new mechanic did it for free - he did not want the stuff floating around in the air!)

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

You obviously misunderstood. I don't disagree about R12, I am merely stating facts. Since you were committed to following the chapter and verse of the law, I was merely pointing out a few things that I thought you would want to make sure that you know.

Chill out.

looks like I am sold on retaining the R12 system. so, right now, due to compressor leaking, I am told that there is no R12 left in the system. The system now is 'Flat'. I plan on replacing the compressor, drier and expansion valves. Any tips on the procedure on how to go about it? I have dealt with a lot of DIY on my 91 560SEl but this will be the first time for an AC rebuild for me. After changing all parts do I still need to evacuate before it can be re-charged with R12?

There a a few re-built compressors sold on EBAY. Are these any good?

thx,

After a system is opened for service it must ALWAYS be evacuated, and THOROUGHLY so before charging.

The question would be whether or not the system needs flushing. Was the compressor only leaking, but working okay and without noise? If so, then you will not need to flush the system. Since it was originally R12 and if you know for sure that it has never had any other refrigerant then you are golden. Simply replace the compressor and r/d, add a few ounces of mineral oil, evacuate and charge.

I have used a few compressors bought on ebay with good success. Most of the MB ones can be had as a kit that includes the new r/d in the package.