Can anyone suggest the best steps to take to overhaul my ac. I've gone through 2 compressors and would like this one to last. I know that I should replace the dryer. Is there anything else that should be done? I plan on buying a rebuilt unit since I have not had any luck with all others so far. I don't want to waste good money on a new one if its not going to last. I first need to replace the hose that runs through the fire wall. It is leaking at the front connection. Should I flush out the system? If so, what do you reccomend I use? Thanks in advance.

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85 300TDT 456,000 orig. miles

If your compressors are going bad, there is a good chance you have particles from the compressor in the system. The only way to be sure the system is clean is to flush every component very, very, very thoroughly with compressed air and a/c flush (although you can use odorless mineral spirits). While the system is open you should replace the reciever drier (this, by the way, should be the last part you put in the system before you button everything up and pull a vacuum on it. If the r/d is opened and allowed to be exposed to open air for any length of time, or installed in the car and you don't pull a vacuum immidiately, it will be wrecked), as well as install a filter on the vacuum side right before the compressor. This will catch anything you didn't get out during the flush proceedure.

Might as well through in a new expansion valve while you have the system open.

You can get all the parts you need at www.ackits.com.



GregS

If the compressor or the RD have contaminated the rest of the system.... the factory shop manual says that the pipes at the compressor are to be replaced... they suggest that due to their interior shape they can not be cleaned by normal flushing.
This was news to me... I must stop sitting around reading the AC manual....

When every you replace a failed compressor-

You are faced with metal in the system. I've pulled pieces of the compressor out of the lines which are quite sizable- the size of your finger tip.

It is customarly to flush heavily! So, you need o-rings and take the system apart as much as possible and flush each part. Always replace the expansion valve. It's a place for metal to collect, and any damage or leakage would require taking the system apart again.
I prefer something a little stronger than mineral spirits. Naptha or acetone, but everyone has their preference. Put a slug of liquid in the line and blow it through the system. You'll need some rags in a container on the other side. Repeat until you get all the old oil and residue out of the system. It should come out clean... You'll need to add oil to several parts of the system. Button it all back together, evacuate and fill. Your probably looking at $400-500 in parts.

This is the time to replace or rebuild hoses(depends on weather you are talking high or low side). Look for leakage(oily hoses). It's also a great time to replace the firewall seal were the lines go through.

I've got a seal FS if you are interested.


Sincerely,

Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

Speaking of stuff being left in the system after flushing....
The Factory Shop Manual says if there was system contamination of that sort that the pipe manifold at the Compressor is to be REplaced... it seems that is has internal cavities or turns which are not able to be cleaned by flushing.

Leatherman,

Yes, that's true to maintain warrentee on an MB compressor. I've flushed more than a few and not had failures. My last one was at 125,000 miles and still going. That's good for Texas=)

Some ppl add a filter on the return line before the compresor too. Big thing is just flushing really well. Obviously, he can buy a compressor, manifold hose, dryer, and expansion valve from mercedes. Assy and if the compressor dies within 2 years- mercedes will pickup the tab.

Oh- make sure to clean (I replace), the sharder valves. Little bits of metal will hang in those openings.

I'm not aware of "internal passages in the R-4 manifold pipe", but are you mixing with the Nipendenso compressor manifolds??

Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

Where are "the sharder valves" located in the system? Thanks

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85 300TDT 456,000 orig. miles

I am just reporting what the factory shop manual says....

There are 2 Schraeder valves on the R12 system (we're talking 123 chassis here). One is within a few inches of the thermostat on top of the a/c line that "returns" from the vehicle cabin. This is the "lo-side" valve where one of the guages is attached during diagnostics.

The "hi-side" fill valve is behind the alternator, its hard to see if you don't know where to look.

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

Does anyone know if the a/c line that "returns" from the vehicle cabin can be rebuilt, or do I need to go to mercedes and bend over? I noticed a leak on the top of the line towards the front of the engine. Thanks

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85 300TDT 456,000 orig. miles

Those are the lines you get rebuilt!!!

The line from the condensor to dryer or dryer to expansion valve are cheap and you *replace* them.

There are two sections where you are discussing. One runs from the expansion valve by the airfilter housing. Then connects to the one firmly mounted infront of the valve cover, which has a flex section down by the side of the ps pump. If memory serves correct.
Shrader valves should be obvious on the 1985 model- one right close to the t-stat housing, one lower near the back of the alt/engine mounting bracket(??? Memory is fuzzy on that one-maybe I'm thinking of my 81').


Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

Break every single connection and then flush, Flush, FLUSH and then flush EVERYTHING. Follow all this up with a good and THOROUGH flush.

Good luck,
PS: Don't forget to flush. LB

Larry, If one were using a recycling flusher.... how long would a good flush take ? I am talking each section if one is not using the old combo valve and doing it all at once...

I don't know. I've never had the luxury of flushing with any method except breaking everything apart, filling and pressurizing my flush gun and then going at it.

The fancier methods probably work well and fast, but I would personally want to flush in both directions.

Have a great day,

Larry, Did you ever get that hose crimper ?