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  #1  
Old 09-24-2009, 07:58 PM
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AC Recharge

Noob to AC work..........

OK, so I have finally gotten my '87 300D put back together after I crashed the front end back in July. Replaced radiator, fan clutch, AC condenser & put G-05 in cooling system (after flushing, of course).

Now it's time to recharge the AC. It had been converted to 134a by a previous owner & I am going back to R-12. I have gauges & freon. Also borrowed a vacuum pump & can tap. As far as I know compressor is OK, but don't know if it or expansion valve were changed in the conversion.

What exactly is the procedure for recharge? I searched & results crossed my eyes, mainly dealing with 123s, but mine is a 124.

Is this right?

1. Pull vaccum & test for leaks.
2. If doesn't hold vaccum, charge w/nitrogen & R-22 (small charge) & check for leaks.
3. Fix leak(s).
4. Recharge w/R-12 compliant oil.
5. Recharge w/R-12 to 2.4 lbs (per label in engine compartment).
6. Enjoy!

I have already flushed system to get rid of 134a oil & installed new dryer.
Anything else? Is there any pressure reading on the gauges I should know about?

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  #2  
Old 09-25-2009, 09:49 AM
LarryBible
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It sounds as if your research has been thorough and worthwhile. Your plan sounds pretty good.

You need to go ahead and evacuate as soon as possible since you've already installed the new drier. As soon as you unseal it and put it into the system it is buisy soaking up system moisture. Getting the moisture out, at least most of it, is best done with the vacuum pump, so as not to swamp the new drier.

Good luck
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  #3  
Old 09-25-2009, 10:06 AM
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Unless you have a charge machine it is going to be difficult to put exactly 2.4 lbs in. You will be able to estimate using the weight on the cans (assuming you are using cans versus a 30lbs keg) but make sure you watch the pressures on the gauges and refer to a temperature/pressure chart.

Some say that you can't check for leaks under vacuum. Obviously if it leaks under vacuum something is wrong but some say it can hold vacuum and leak under pressure. You may want to check for leaks with the system under pressure (nitrogen) anyways, but I've never done it that way. The systems I have worked on that have leaked have shown leakage under vacuum.

Otherwise everything sounds good.
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  #4  
Old 09-25-2009, 11:03 AM
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Your manifold gauges often have a temperature/pressure "chart". I just purchased a set yesterday that is specifically for R-134a and the guages still have the R-12 charts.
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  #5  
Old 09-25-2009, 12:59 PM
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Thanks, guys...

LarryB - agree with you on pulling a vaccuum ASAP to protect the new dryer. Will be doing that today. I might also add that your advise is what prompted me to go back to R-12. Found 6 cans @ $10.00 each.

Graplr - my initial check under light vaccuum show possible leaks, but I have also heard that systems may leak under vaccuum but not under pressure. I have a friend coming by today with nitrogen & R-22, as well as a leak detector, so maybe we can find where the leak is.

Gene Horr - the gauges are borrowed from a friend in the home AC business & have no pressure charts. He's out of town now & really is not into auto AC systems. Is there somewhere online & can find them?

On Edit: Gene, I found a good chart here for others that might need it: http://www.peachparts.com/shopforum/showthread.php?t=150971

Last edited by dagObx; 09-25-2009 at 01:05 PM.
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  #6  
Old 09-25-2009, 01:58 PM
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Quote:
Originally Posted by dagObx View Post
Graplr - my initial check under light vaccuum show possible leaks, but I have also heard that systems may leak under vaccuum but not under pressure. I have a friend coming by today with nitrogen & R-22, as well as a leak detector, so maybe we can find where the leak is.


On Edit: Gene, I found a good chart here for others that might need it: http://www.peachparts.com/shopforum/showthread.php?t=150971
That is the same pressure chart I have used.

If it leaks under vacuum, there is probably about a 99% chance it will leak under pressure. Glad you have a leak detector. I bought one this summer and it made finding the leak in my SDs system much easier.

Fix that leak before you put those cans of R12 in there!

6 cans for $60 is pretty good but I got a case for $60 2 years ago and I bought a 50lbs keg (maybe 1/2 full) of recycled R12, a 30lbs keg with about 3 lbs left in it along with a charge machine and a reclaim machine all for $100 at the end of the season last year. A shop was getting rid of all their R12 stuff. I've already gotten my money back.
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1985 300CD
1981 300TD


Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD
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  #7  
Old 09-25-2009, 08:44 PM
LarryBible
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Yes a charging scale would be nice, but 2.4 pounds is right at 39 ounces. Three cans is 36 ounces which would be close enough.

Hopefully the Nitrogen, R22 and sniffer located your leak. Don't plan on a leak under vacuum not leaking under pressure.
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  #8  
Old 09-26-2009, 12:25 AM
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OK, so far so good - I think. Pulled vacuum on system down to -24 in Hg late yesterday. Went back & checked (car still at indy's) this afternoon & it still had -22 inHg. I took that for a good thing.

Put oil in system (using vacuum to suck it in [4 oz.]) & tapped one can of R-12. Can tap was screwed up, leaked most of it out. So I stopped until I can get a good can tap. R-12 too hard to get out here to just let it all evaporate due to a bad can tap. I have a couple of friends that might have what I'm looking for.

Will go back to it tomorrow (Saturday) after I get a different can tap that doesn't leak!
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  #9  
Old 09-26-2009, 07:51 AM
LarryBible
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To begin with, you should draw a 28" vacuum. If the system is tight, it will still hold 28" after whatever period of time you let it set.

Good luck
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  #10  
Old 09-26-2009, 10:08 AM
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dagObx, You need to reread the posts by others in this thread... and perhaps do some more reading on other sites.... you are getting close....but not really understanding the criteria which you need to be shooting for. In other words... Not good enough so far...
Try tightening all your connections gently with two wrenches and re vacuum and pressure check before proceeding.
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  #11  
Old 09-26-2009, 10:45 PM
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Why didn't anyone in this thread advise him to drain the oil that was used with the 134a?
Isn't that a high priority due to lack of compatability of 134a oils with R12?
Not an AC pro, but I've read a lot on this forum!
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1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html
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  #12  
Old 09-26-2009, 10:53 PM
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Quote:
Originally Posted by Graplr View Post
If it leaks under vacuum, there is probably about a 99% chance it will leak under pressure.
The implication works only the other way. If it leaks under vacuum, you can be absolutely sure that it will leak under pressure.

And it's been said in this thread already, but 24" is not even close to enough vacuum. You won't boil water out at that pressure (unless it is very hot out, but you would be dead at this kind of temperature).
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  #13  
Old 09-27-2009, 09:32 PM
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Quote:
Originally Posted by Cr from Texas View Post
Why didn't anyone in this thread advise him to drain the oil that was used with the 134a?
Isn't that a high priority due to lack of compatability of 134a oils with R12?
Not an AC pro, but I've read a lot on this forum!
We wanted to leave something for you to add to the thread....

I assumed he had gotten rid of it when he put ' recharge with r12 oil ' ...
but I should not have....
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  #14  
Old 09-27-2009, 10:25 PM
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I've read that the new DEC-PAG will work with R12.
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  #15  
Old 09-27-2009, 11:13 PM
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Thanks, guys/gals..

I've had to put this on hold for a few days as the person that loaned me the gauges needed them back. I'll get back on it sometime next week.

To clear up a few things:

1. I flushed the system to get rid of the PAG oil or whatever was used for the 134a.
2. On the vacuum, the gauge only showed 24 in Hg after pulling a vacuum for over an hour. The next day it was 22 in Hg, so said the gauge.

LarryB - I hear you on the 28 in HG, but I could never get it above 24 in HG - the pump just wouldn't pull it that low. And it's a pump the guy uses professionally in home heat pumps, so I don't think it has a problem. I am beginning to think the gauge could be innaccurate, something was said that there might be a problem with the low-side gauge. I pulled a vacuum on a reclaim jug in case I have to start over & the pump pulled it down to 30 in HG, so I don't know what to think. I do have 1 can of R-12 in the system I don't want to lose.

All - thanks for your help, I know I don't have it just right yet. Got more to do. I will he checking for leaks with the sensor when I get the gauges back. Also have access to some nitrogen & R-22 if I have to do some serious searching.

Will check back with results.

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