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
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 find suppliers of Freeze-12 with
complete kits for about $60 including the Freeze-12 refrigerant and
fittings if you want to try just charging the system yourself. That
is what I would do, but since I have had my system completely apart I
have to get it evacuated and that takes a special machine.
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
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. Fixing the leak is the same cost (parts, labor), not related
to the type of refrigrant.
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 components to fail when they
would continue to operate normally with R-12 or even Freeze-12 which
has pressure curves more like R-12 than R-134a has.
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).
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
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
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.
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.
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