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Old 09-20-2003, 07:33 AM
Registered User
Join Date: Aug 2003
Location: San Juan, PR-USA
Posts: 92
Tough decision A/C unconversion

Hello friends. I am asking for advice regarding the improvement of my A/C system in my 350SD. I've been reading a lot about the pros and cons of R12 and R134a. I even became certified yesterday with tha 609 Cert. (Thanks to all of you). I want to go back to R12 if that will imrpove my marginal system, but flushing the system gets complicated when you get to the old Nipondenso compressor. ACkits states that compressor should not be flushed, it should be replaced ($625.00). Is it ok to flush everything and just blow some air through the compressor? If it is that difficult, will it be better to replace the A/C condenser with a parallel flow in a W126 and stay with R134a? If that a better solution which size is the optimal for a W126? I am more incline to do the R12 unconversion but I need to clarify the flushing issue.

Thank You again in advance. I am enjoying the forum and hope to help others with my limited experience.

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Old 09-20-2003, 07:56 AM
engatwork's Avatar
Join Date: May 2000
Location: Soperton, Ga. USA
Posts: 11,235
Was the car originally r12? If it were not then it is probably designed to do a good job on r134. If it is not performing up to spec on r134 then it may be something not quite right with your a/c. On the other hand if it were r12 originally I would definitely go with r12. I'd have to look up in the manual what it says about that particular compressor in regards to being able to flush it out. If no one comes along and gives you a definite answer pretty soon I will read up on it and let you know.
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Old 09-20-2003, 10:40 AM
I told you so!
Join Date: Jun 2002
Location: Motor City, MI
Posts: 2,741
Darrel, a/c compressors - both old and new - are typically flushed by the following procedure:

- Remove compressor from vehicle.

- Hang compressor so lubricant drains from it. Rotate the shaft every once in a while to get as much lubricant out as possible.

- Pour in some new fluid. Run it through the compressor by rotating the shaft. Let that fluid drain.

Don't use compressed air in the compressor.

If you need more help with your a/c I recommend posting questions at , a site devoted to automotive air conditioning systems.
95 E320 Cabriolet, 131K
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Old 09-20-2003, 04:26 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Good compressor flushing method.

There really isn't much oil in Nippondenso compressors anyway. other concept to ease to process is that it is now recognised that the various oils do not interfere with each other. The concept being that the proper oil is required to be miscible in the refrigerant used. The other oil won't mix and just winds up sitting around in the corners. Just have enough of the oil required.

Jim was right though, 126 cars do decent in 134. They do have some chassis specific failures though. Poor AC is often dirty, blocked evaporators (air goes around not through enough for cooling) or a fully open recirc door will knock 10-15 degrees off duct temp.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 09-20-2003, 06:39 PM
dmorrison's Avatar
Registered User
Join Date: Dec 2002
Location: Colleyville, Texas
Posts: 2,694
Our 300SDL gave us problems with the AC system. It just wasn't cold enough. The dealer wanted to replace the expansion valve. 12 hours of labor plus parts and suplies. I nixed that because they were not sure that was the real problem.
The expansion valve is behind a cage that was built around the steering column for the airbag.
Someone made a tool to get to the expansion valve without taking the steering support out. Do a search

I feel the problem we had was the ETR control. The AC would work great sometimes and poor to nil others. All this while the pressures were OK.

The Idea of a blocked eveporator I will agree. Heres the link to a pict of my 123 eveporator.

evaporator out of the 300TD

Lots of blockage.

As steve said, check your vacuum elements.

1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car
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Old 09-20-2003, 09:53 PM
jbaj007's Avatar
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Join Date: Jun 2001
Location: Santa Monica, CA
Posts: 2,053
Never have done an evaporator (fear factor ). Does the evaporator sit behind the heater core directly or a little below the heater core? I didn't look closely when I had the fan removed; can I see the evaporator off to the left if I pull the fan/housing only? I'd sure like to spray some foam A/C cleanser in there after seeing your picture. This is on a 126.
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)
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