I used the original hoses. I changed the receiver/dryer, exp valve, seals, and added the R-134a with esther oil.

From what I have read they found that hoses which had already had oil in them from R-12 would hold 134a without leaking... but new hoses would need to be the barrier type...
So I think if you just flush well both directions... you can recycle the first flush, then end up with new flush last on each item... you should be fine. Blow dry as best you can and it is nice to do this very close to putting the system together... at the very least after drying as best as you can cover all open ends until you put it together. Just like you would treat the new reciever/dryer....keep closed until the last possible second.

Okay, thanks. I need a new compressor anyway, the original one is making lots of noise. But new hoses will better than double the cost of the job, so I was hoping to avoid that expense.

Section 609 is what you need to be able to work on MVAC and buy small R12 cans (608 is needed to work on sealed/stationary systems). Check out epatest.com (there's other sites too). Like everyone said, passing the online test is pretty easy. Having 609 certification won't satisfy everyone of course. For instance, in order to buy R12 in the City of Austin, one has to get a special license from the City of Austin (in addition to the 609 certification) -- or drive 15mi up the road to Cedar Park, and buy it there.

Regarding barrier hoses: I've read that while it's generally recommended to use barrier hoses on R-134a systems (due to smaller R-134a molecule size), it's actually perfectly fine to keep existing non-barrier hoses during an R12->R-134a retrofit, because the hose body would have absorbed enough oil to make it effectively impenetrable by R-134a.

I thought if the compressor takes a dump you need to replace the receiever dryer too? I would think that if you pumped the system up, ran it for a few minutes, apply vacuum to the system and suck up everything, recharge and run it for a few days and then run a vacuum on it and then change the reveiever dryer, you are ok? My reasoning is that everything goes thru the R/D which is a filter. The first time you run the system for a while, you are blowing whatever debris into the R/D. Suck it all out then and refull the system. That should get most of it out. After driving it for a week, if you suck it all out again and then replace the R/D, you should just about get everything. However, if anything is left, it gets to stay in the R/D and should not be a problem. this was told to me by an automotive instructor who teaches AC work.

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99 E300 Turbodiesel
91 Vette with 383 motor
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03 SeaDoo GTX SC Red
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"I thought if the compressor takes a dump you need to replace the receiever dryer too?"
Anytime your system is opened up you need to replace the R/D.

"vacuum to the system and suck up everything,"
You really can't do that because the R/D has dessicant in it... to get and keep the very last moisture possible in the system. You can not get the moisture out of the oil load and dessicant in the R/D by vacuuming... .thus the suggestion that it must be replaced instead of ( for instance ) just vacuuming it to a certain spec...

"Suck it all out then and refull the system."
Most people do not have the expensive machine ( or a homemade version either ) to hold the R-12 while it is out. Would be less than frugal to loose the first charge and have to put in new R-12 when the standard operating procedure works fine.

I don't know what that AC instructor was thinking.... or what books he was consulting.... if you still know him you might ask where he has seen that concept recommended in writing... all the features which I have described here I can show you the sources from Multiple references...

"That should get most of it out."
The effects in terms of degraded system and potential for acid production is such that we are shooting for ALL of it out... as far as our procedures and equipment will accomplish....

" it gets to stay in the R/D and should not be a problem."
The R/D has a rather small capacity... is a one way function in terms of contamination... this is why the rule is to replace.... and replace at the last possible moment with regards to the system being clean...the R/D hopefully takes up the slack on anything left and holds it safely.

Here is the link to sec 609, automotive certification.

http://www.epatest.com/

__________________
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2001 Dodge Stratus (Silver) (wifes) 55814 miles...

1982 280TE Wagon Astral Silver Metallic/
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Einigkeit und Recht und Freiheit

The answer to the original question is a definite Yes. Do flush the evaporator, but don't use AC flush, use acetone. Thanks whunter. I'm glad I flushed mine, a lot of bad stuff came out. There wasn't much oil left in the system, but apparently most of what was there found its resting place in the evaporator. A good portion of those 8 UV dye applications ended up in the evaporator, too. The first five batches of acetone came out brown and nasty; there was some solid stuff there too.

I really don't understand what the deal is with that "AC flush&clean" liquid (made by Interdynamics, bought at O'Reilys). It's not an organic solvent, it's more like an oil. If your pour some on a piece of paper, it won't evaporate. After it's used to flush a hose, it remains in the hose, and subsequent blowing of air through the system doesn't remove the liquid from the hose completely. You blow air for minutes, and small droplets of liquid keep coming out. Acetone is really different in that regard: you blow it out with air, it comes out quick, and then it stop coming out. I reflushed the condensor with acetone, and that helped to get all that AC flush liquid out. Still, it's probably unsafe to use acetone on non-metal parts. It would seem like there should be some AC flush that actually evaporates cleanly and completely, like acetone, but doesn't destroy plastics, like acetone does.

I have been told there are now several replacements for R-12 that are much more efficient than R-134a. So you can still have the efficiency or better of R-12 with stock compressors and still be eco-friendly. one name to check for is hot shot

mercedes 300td

Do a search on those and you will find out why those are all crap for one reason or another................

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Proud owner of ....
1971 280SE W108
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1983 300D W123
1975 Ironhead Sportster chopper
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

The replacements are either a blend or a flammable. The flammables are not wise not only due to their flammability, but also the fact that they will not circulate the lubricant as it should for goood compressor life.

The blends are a pain because the only way to recharge if you get a leak is to empty the system and replace ALL of the refrigerant. Also, due to the different components it is sometimes difficult to get a lubricant that will properly circulate with the blend.

There is just no need to use them. R12 is coming down in price. About a month ago, I bought a 30 pound cannister, delivered to my door for $425 total cost. That is less than $15 per pound.

Good luck,

WHunter, This is four years later... are there not any proper flushes which you would recommend now ? Instead of the acetone ?

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

There are a few products 90% as good as acetone, for double or triple the cost of acetone.

Pure ether is as effective as acetone, but is far more dangerous...
http://www.google.com/search?hl=en&rls=com.microsoft%3Aen-us&q=100%25+ether+msds&btnG=Search&aq=f&oq=&aqi=

http://www.google.com/search?hl=en&rls=com.microsoft%3Aen-us&q=99.99%25+ether+msds&btnG=Search&aq=f&oq=&aqi=

http://www.google.com/search?hl=en&rls=com.microsoft%3Aen-us&q=99.99%25+ether+danger&btnG=Search&aq=f&oq=&aqi=

The factory service manual for the Jetta says to use 134a to flush the system, using closed-loop equipment which is made for this purpose. It's the first I've ever heard of that.

They also consider 78% - 90% clean is good = gets you beyond warranty.

VW service procedure has what relation to Mercedes Benz ?