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  #16  
Old 04-22-2003, 07:43 PM
agood's Avatar
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Location: Roswell, GA
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Well, I think I found the leak....I appears to be around the expansion valve. I could see the UV dye but there was much less than I expected......I hope this is the only leak....all 2.5 lbs have leaked out in less than 24 hours.....
Anyway, do the expansion valves go bad or should I just replace the O-Rings and reinstall it....The O-Rings do appear to be bad and the leaks appeared to be around the fittings....

While I have the system open I want to flush the ole oil and put in new oil....how can I do that and how much oil should I put back in?
Thanks
Brian
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1995 E300 Diesel
1994 E320
1999 C230K
1994 S500 W140
1990 300 SEL
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  #17  
Old 04-22-2003, 07:47 PM
Holson Adi's Avatar
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Location: Boston, MA
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My A/C leak has been getting worse and worse and my mechanic couldn't find the leak. However I'm not sure if he really looked for it. I think I'm gonna take it to somebody else. He's done good work on everything else but my A/C problem is never fixed.....
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  #18  
Old 04-23-2003, 07:35 AM
LarryBible
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You should be able to examine the expansion valve and determine if it is leaking at a connection or at the bulb. I had one fail a few years ago and was leaking freon around the bulb. If that is the case you have to replace the expansion valve. If it is leaking at one of the connectors, then new o-rings with the nylog sealant should fix it.

Since you're planning on peeling the system apart anyway, you might just buy an R134a expansion valve. This is one that replaces the original and is calibrated for 134.

To flush, you would be best served by purchasing a flush cannister and gun from your automotive a/c supply house. You take the top off the cannister and pour in the flush agent. You put the top back on and pressurize the cannister with compressed air through a shraeder valve. There is a hose and blow gun. After disconnecting all the lines, you put the blow gun at the lines, condensor and evaporator. Blow in some flushing agent then blow it out with compressed air.

This is best done on a hot, dry day so that you get as little moisture in the system as possible. MAKE SURE YOU BLOW ALL THE FLUSHING AGENT OUT OF THE SYSTEM. After thoroughly flushing everything and BLOWING ALL THE FLUSHING AGENT OUT OF THE SYSTEM, you then put everything back together with 134 compatible o-rings coated with nylog. You can get an assortment of 134 compatible o-rings and nylog from acsource.com for about $25.

Once you have flushed everything, resealed or replaced your expansion valve, and buttoned it all back up, you need to pull a good vacuum on the system for as long as possible under the warmest conditions possible. If it is not a HOT day, it wouldn't hurt to use a heat lamp on the evaporator and condensor to help boil out moisture.

DID I MENTION THAT YOU NEED TO ENSURE THAT YOU BLOW ALL THE FLUSHING AGENT OUT OF THE SYSTEM?

Make sure you have really looked over the system with your black light to be as sure as possible that this is your only leak.

As you go through the process, let us know if you have any more questions. You would be well served to find a local automotive a/c supply house to get flush cannister, flushing agent(some people use mineral spirits, but they leave a residue) and whatever you might need.

Good luck,
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  #19  
Old 04-24-2003, 01:30 PM
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Larry, Help!

I have just picked up an 87 420 SEL and I am having a similar problem with the AC also I don't know the history of the AC but it does not come on, is there a safety catch that will not allow the compressor to kick in when there is no freon in the system I jumped the compressor and it does turn on could it be that there is no freon in the system and it will not turn in order to protect it self? It is still using freon I am assuming. Could I convert the system over to R134A? Is it something I can do on my own? any help would be appreciated.
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  #20  
Old 04-24-2003, 02:44 PM
agood's Avatar
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Location: Roswell, GA
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There is a low pressure cutoff switch on the dryer....next to the radiator in my car....you can pull the wires off the switch and jump them together and the compressor will come on....be careful...you want to make sure there is oil in the system.


To continue with my story.

I replaced the Expansion valve and the dryer (with both new switches) and connected the vacuum pump and it still will not hold a vacuum. So, I still have a leak somewhere.....all I can think of now is the evaporator....as big of a pain as the expansion valve was I hate to think about replacing the evaporator.....
Any words of encouragement?
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1995 E300 Diesel
1994 E320
1999 C230K
1994 S500 W140
1990 300 SEL
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  #21  
Old 04-24-2003, 02:52 PM
LarryBible
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REDLARK,

Yes, you are most likely low on refrigerant. There is a low pressure switch that interrupts the clutch circuit because there is no oil circulating when refrigerant is low. This saves the compressor.

You need to find the leak and recharge with R12. MB's do not have the reserve capacity to convert well. To properly convert you should completely dismantle the system, THOROUGHLY flush out the mineral oil, replace the filter drier, pour the old oil out of the compressor, put in the correct amount of ester oil, put on 134 adapter fittings, evacuate and charge.

There are kits at wal-mart to convert at home, but these are called death kits by those familiar with auto air systems. Not to death to the person but death to the a/c. They will often make cold air, but usually not for long.

Good luck,
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  #22  
Old 04-24-2003, 04:06 PM
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Thank you

Thank you very much for the info I must say I have never owned a car of this calibur before but I am happy to admit that I will forever be a mercedes lover. It is very refreshing to be able to come on to a sight where every one is very willing to help out no matter how small of a problem you have! Thank you very much
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  #23  
Old 05-01-2003, 10:24 PM
agood's Avatar
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Join Date: Apr 2003
Location: Roswell, GA
Posts: 198
Larry,
Well I got the system running for about 2 days and it leaked down again....I kinda figured it would because it would not hold a vacuum.....BUT the dye helped and I found the other leak at the compressor....so I replaced it....
Now it holds a vacuum so I should be ready to go.....at least I thought I was.....
I pulled a vacuum on the system for about 1.5 hours.....and then recharged.....my high pressure is around 250 and the low is about 40.....but it is not cooling....at least not very well....
The only thing I can think of is I did not leave the vacuum on long enough....think that is the problem?
Thanks
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1995 E300 Diesel
1994 E320
1999 C230K
1994 S500 W140
1990 300 SEL
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  #24  
Old 05-02-2003, 08:36 AM
LarryBible
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agood,

If you did not thoroughly evacuate, that is a bad thing, but if it mostly evacuated it should not keep the system from cooling. Although those pressures should be providing good cooling a converted system will sometimes be elusive when trying to charge to the correct level. I don't even remember what model you are working on, so I don't remember if it is an original 134 system or converted.

Also when you have seemingly good pressures, blower running and everything else pointing toward a properly running system but it is not cooling well, don't overlook the possibility of heat being added to the system. On most models this is controlled by a monovalve or heater control valve near the battery. If it is an early eighties car the valve can fail open. On later cars the controller will fail causing the valve to flow when it should not.

With the a/c on full, feel of the hoses in and out of the valve. The one entering the valve from the engine should be warm and the hose on the other side toward the heater core should not be warm. If they are both warm then the valve is flowing hot coolant to the heater core offsetting the cold air from the evaporator.

Keep on plugging at it.

Good luck,
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  #25  
Old 05-02-2003, 09:48 AM
agood's Avatar
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Join Date: Apr 2003
Location: Roswell, GA
Posts: 198
I thought about the heater valve and checked and it was functioning properly.

Should open the system again and then evacutate it again for a longer time?

It is a converted system. I have noticed that the flow thru the sight glass in the dryer is white/milky looking.....is that a sigh of too much moisture?
Thanks
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1995 E300 Diesel
1994 E320
1999 C230K
1994 S500 W140
1990 300 SEL
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