I don't know why I like this car so much but I do, it's a love hate
relationship. I have been beating the problems out of this car one at
a time and now when I think I am at the end of any thing else that
could go wrong I find that I have no AC. The R12 is all gone suddenly
I am in the HVAC business for a living and work with air-conditioning
every day but not on cars. I have determined that I have a leak in the
evaporator. There is a strong detection of refrigerant coming from
inside of the evaporator box. There are no leaks about the expansion
valve, I am getting a strong detection from the openings of the
evaporator housing and the detector will go off when sampling the air
from the vents when the blower is first turned on. I am quite
surprised that a copper evaporator could leak but it seems mine is
Not wanting to put more R12 into this car at this time, I have blown
out as much mineral oil as possible and replaced it with ester oil then
charged with 134a for now the car cools OK but I am sweetening the
charge every 3 days to stay cooling. My plan is to replace the
evaporator and re-service the system with R12 when the system is leak
Now to the part I need help with, this looks like a hell of a job, as
best I can see the entire insides of the front of the car will have to
be removed in order to get at this evaporator. I have looked at my
Benz Shop Manuel CD and can find no instruction on this procedure.
I am hoping that someone has in print the step by step procedure for
this job or If any one has actually changed an evaporator in a 126
body before could they tell me what they can tell me about this job?
Any help will be seriously put to good use,
BEFORE you tear into the evaporator .....
Take a look at the very top of the receiver/dryer. There lives a brass
plug that has a small "blow out plug" soldered into its center - which
"blew out" on my '80, not too long after its R-12 was recharged. It was
resoldered and the R-12 refilled and hasn't acted up since.
I am looking for any way out of this that I can find but the fact
remains that refrigerant is only detected at openings to the evaporator
area. I have gone over the whole system with an H10 type electronic
detector. It raises no indication of refrigerant leakage at any point
except the evaporator. My detector yelps and squeals as it is poked
into the duct next to the drivers well. I have am leaking about 6
ounces a day witch would be awfully hard to over look that size of leak
in an open area such as around the receiver. I plan as a final test
before jumping into the evaporator to isolate it alone with fittings
and do a pressure drop test with dry nitrogen.
It is frustrating to not be able to get at the evaporator. I work on
air conditioning equipment daily but am able to see and reach all parts
of the systems we work on. R&R time on a typical residential systems
evap coil is about 45 minutes plus about another couple of hours for
proper evacuation and servicing and adjusting the system properly. It
looks like my car will take many days for the same.
I do want to make sure of this diagnosis and will recheck the fuse plug
at the receiver before going off the deep end but for now I am trying
to get a scope of what is involved with changing this evaporator
because for now that's what it looks like it's going to be.
By the way I discovered this lack of air conditioning on the test
drive I took last week just after putting in my second tranny from the
junk yard. Good grief! The good news is the second tranny goes right
into 4th ok. Some day I will get every thing to work at once.
Thanks for the post, I seem to have car exhaust coming only out of my
evaporator box, LOL. I am sure that it is refrigerant that I am
detecting and short of finding any other leak after rigorous searching,
I seam to get a strong detection at all entrances to the evaporator. I
am using a very high quality sniffer that only alerts on a narrow
selection of refrigerants. I am not trying to be a know-it-all but I
have been looking for and finding leaks for 40 years. What has me shut
down is I have no experience with this particular leak situation so I
am looking for help with any idea that will explain what I am finding.
Keep in mind that I plan to do an isolation test of just the evaporator
before I would invest the labor of changing it. I need to find the
fittings soon, I probably will modify an old expansion valve so I can
pressure up the evaporator with nitrogen, if it drops then that will be
my final diagnosis. In the mean time I believe I have a bad evaporator
and am looking for the grand procedure of how to chang it. With so
much stuff to remove and replace it would help if one would know the
fastest order to proceed in.
Thanks again for the post as any comments are greatly appreciated.
Welcome to Mercedes dirty little secret: HVAC. The older ones barely
work at all and the newer ones, while pretty good seem to have the
car built around them. That's because they do.
Replacing a 108 heater fan or any halfway modern heater core
is a long and tedious job. I have a receipt for replacing the
heter fan in my 108 from the PO he had done in 78. 40 hours labour.
Need Mercedes parts? http://parts.mbz.org
Richard Sexton | Mercedes stuff: http://mbz.org
Richard Sexton wrote:
car will take many days for the same.
In all fairness to MB, is it any easiery to replace a heater core or
evaporator on most other cars? Because of where they are located, it
isn't ever going to be easy.
As for the blower, I'm not familiar with the 108, but if it takes 40
hours, I agree that sounds like a bad design. On my 116, it's maybe a
2 hour job. You have to take off the right hand lower access panel and
remove the glove compartment. But then it's right there in your face,
held in by 3 easy to get at screws. That design covers a lot of cars
cars, the 450SEL, SE, 6.9, 280SE, 300SD, from 1973 to 1980.
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