Air Conditioning 1991 300E

No... it doesn't make sense. Just go to autopart store and get their leak dye detector... and just inject it into your system... and look for the dye.

The fill ports of high and low side must have cap on it... or you will simply lose out alot of freon.

Last spring I had a local shop recharge my system and leak check it. They connected it to vacuum, decided there were no leaks after it held vacuum for 1 hour, filled the system with R-12, charging 30 a pound for two pounds and $90 an hour for labor, the total bill was $212. The charge leaked out in two days.

So I took the car to a better shop that specializes in AC I have used before in Las Vegas. I had a "hisser," a hose that was blown and leaked so badly they had to replace the hose before they could fill the system to do a leak check. They put an inexperienced kid mechanic on my car, a 1982 300 TDT I have restored to like new condition, but don't expect a 22 year old to appreciate that an old car is anything but junk. He did a lousy job building a replacement hose instead of getting it as a part from Mercedes. That job, with the 2nd recharge was $516. Two days later the hose the kid built burst and that was the end of that charge of R-12. That shop has one of those sophisticated machines that are able to detect where leaks are in the system, and it had detected slow leaks on several hoses and my condenser, so I was kind of surprised that the kid went ahead and charged the system and I wasn't surprised when his hose burst because the metal fitting he had made was all crooked and mangled and had blobs of cold solder all over it.

That place refunded a couple of hundred dollars since the hose blowing was their fault, so I had about $500 down the drain.

I had just put in a new evaporator, which is a big job because you have to remove the dash and the entire unit under the dash that contains the heater coil and evaporator, take that unit completely apart and then remove the old evaporator, put the new one in and put everything back together. It is a 15 hour flat rate job and Mercedes quoted $1,800 just to replace the evaporator for labor only, the part was another $1,800 or something. You can get them for under $300 from discount parts places.

So right now I am replacing all the hoses, which I have purchased as parts as opposed to having my local shop build them, and putting on a new condenser and dryer. I had already replaced the compressor and dryer not long before I did the evaporator, but I am going to change to Freeze-12 refrigerant, so I have to change the dryer again.

I have a quote from a local shop that specializes in Mercedes to evacuate the system, recharge it and do a leak check for between $200 and $300.

So I will have a ton of work and lots of cash in this AC system and I sure hope it works this time.

In general, I would suggest that you prepare to spend a lot of money and replace anything that is starting to leak with good parts or else you will just be wasting your money.

The shop guy, who was very knowledgeable, quoted $100 a pound for R-12, which seems too high, but I am switching to Freeze-12 because it is EPA approved and you can purchase it yourself and do your own recharges once you switch to Freeze-12 from R-12.

If you do a Google search you will f> Well, I had the air conditioning recharged and the Freon leaked out in 2

By the way, the replacement refrigerants, like R-134 and Freeze-12, have smaller molecules than R-12 (freon). So if your system leaks out freon in 2 days, it will leak out the replacement refrigerants even faster because the molecules are smaller.

Also, if your system has leaks that are so bad that it evacuates in two days the leaks are too big for the sealer stuff to work. If you want that system repaired you need to take it to a good shop that has a modern machine for doing a complete leak check.

Find out what is leaking and replace it or you are just wasting your money and damaging the atmosphere by putting freon into the air.

Unless you are willing to work on the AC by yourself, do not use anything other than R-12 or R-134a. No licensed shop will work (including evacuation) on the AC system due to possible contamination to their equipments.

R-134a is readily available and is the cheapest source right now. I converted my 84 190D and 87 300SDL without much replacement (mainly just the dryer, o-rings, oil and R-134a). They both run well after many years. In theory, R-134a is slightly less effective than R-12 but I don't even feel the difference about the cooling effect.

I can't say for sure for W123 body because I never own/work on one but every later MB model (W201, W124, W126) definitely can be converted without changing much hardware.

However, a leaky system must be fixed first, regardless what refrigrant is used. Fix> Last spring I had a local shop recharge my system and leak check it.

Maybe it depends on where you live, but out here in the California desert and in Las Vegas I have not had any trouble finding licensed shops where they are willing to recharge my 300 TDT with Freeze-12. I first learned about Freeze-12 from one of the leading AC shops in Las Vegas, where summertime afternoon temperatures are often over 120 in the shade and there isn't any shade, so AC is practically a survival issue out here. When I go to Vegas I drive through Death Valley both ways, and it gets 130 F (in the 50s C) down there.

When my Benz AC is working properly, it keeps the car nice and cool even on those 50 C afternoons in the blazing Sun. I put a thermometer on the black asphalt at Badwater one summer afternoon. The kind of thermometer that is a round disk with a needle that points to the temperature. It spun around past 120 and just kept going until it registered over 160 degrees F!

The biggest disadvantage of R-134a is that because of its molecular structure it has to be compressed to a higher pressure to reliquify. This higher pressure can cause older comp> Unless you are willing to work on the AC by yourself, do not use

OK, EPA regulation may have changed. I have not followed it in the last

4-5 years after converting my own cars.

Does Freeze-12 use different charging ports like R-134a? Does the shop put special sticker to identify Freeze-12? Or it can be mixed with R-12?

Yes, R-134s needs slightly higher pressure to achieve the same performance but that difference is still well below the max pressure MB system is designed for (at least for the 3 models I mentioned previously).

heav wrote:

A mechanic I spoke to last week argued that since 134a is a Dupont product and the Freeze-12 patent is owned by a smaller, independent company that there is some risk that Congress or the EPA may make some sweetheart deal with Dupont and "freeze" Freeze-12 out of the market. Probably a possibility, but I am not going to worry about that until it happens.

The answer to that is kind of a maybe.

The first time I had my car converted from R-12 to Freeze-12 the shop in Vegas put new fittings on. But the guy who is going to recharge my car next week has the ability to recharge with Freeze-12 without changing the fittings (I have had my car converted back to R-12 at the shop in Vegas, and they have the system back to stock fittings now.).

But you can mix R-12 and Freeze-12. They are compatible in the sense that they both work with the same types of lubricating oil, which is the big problem between R-12 and R-134a that makes it impossible to mix them. Mineral oil and R-134a will turn to a Jello like substance that will require replacement of most of the components of your system if you mix R-134a into a system that has been running R-12 without cleaning the system out first and flushing it to remove the old lubricating oil.

Fortunately I have learned that from reading and not the hard way.

But you are not supposed to mix them, and it is illegal to do so and the installer does have to put a sticker on indicating that the system has been converted to Freeze-12.

I know I am stating the obvious, but if the components are old and not fully up to spec, the additional pressure, I think up to 300 psi from

250 psi, might blow out something that would hang in there with the standard pressure. 300 psi is a hell of a lot of pressure.