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  #1  
Old 07-09-2007, 11:39 AM
dpetryk's Avatar
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Location: Houston, Texas
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Calling all A/C experts

Several problems all related to a 91 420sel.

Replaced compressor, oil, complete flush, new expansion valve, drier, hose assembly, O rings, valves etc. - everything. Using R-12.

1. The pressures on the low side are a little high (55psi) and I was wondering if the expansion valve is not set for R12 but for 134a might be causing the problem?

2. When charging, as I approached 1.5 lbs of refrigerant in the system, the bubbles cleared up. I stopped and checked the performance. It was good. I continued to add the additional 1.4 lbs as per the specification and the pressures were high and the cooling was not as good as it was at 1.5 lbs. The high side was 275 and the low 50-55. I removed 1 lb. and it performed better.

I am questioning the setting of the expansion valve and I wonder if they are not factory set for 134 and it does not allow full performance when using R12.

What do you guys think?

They are adjustable and I am considering setting it to reduce the low sire pressures.

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78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k
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  #2  
Old 07-09-2007, 11:54 AM
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When I replaced the evaporator in my 124, my new EV was labeled as being for 134A. I questioned it and was told that there was no difference.

It works very well in my R12 system.

Are you sure about the weights when you were charging? The idea is to have just enough refrigerant to send a solid liquid stream from the condenser to the EV. That is what the sight glass shows you. If you have good pressures and no bubbles, you should be in good shape.

What were the pressures after you removed that last pound? Did you have any airflow over the condenser when you took the readings?
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  #3  
Old 07-09-2007, 12:12 PM
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Electrons can do anything
 
Join Date: Sep 2001
Location: Houston, Texas
Posts: 1,072
Absolutely sure about the weights.

I had good air flow over the coils (both of them). Engine fan + aux fan + blower on hi.

Pressures after the removal were about 40-45 low, 225-250 high.

I understand about the sight glass as a gauge for filling, however in my experience they need more. They work better when there is more than the sight glass indicates. I live in Houston and performance is key. I own 5 of these things and they all cool better when there is more than the sight glass shows.

AND - why such a big difference when the bubble go away and the recommended charge? Bubble gone at 1.5 lbs. but the system is rated to have 2.9 lbs.
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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k
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  #4  
Old 07-09-2007, 12:21 PM
david s poole
 
Join Date: Mar 2005
Location: dallas
Posts: 1,822
the 275 on the high side is prob responsible for the 50-55 on low side.there is no diff btwn 134 and r12 expansion valves.you need to check that aux fan turning correctly,main engine fan clutch is locking up.assume you vacuumed well before charging.what did you flush system with?all you have said leads me to believe that you don't have enough condensing.either air flow dirty condensor,crushed fins or perhaps dirt between cond and radiator.one other possibility is the fresh air door closing completely?[behind glovebox].
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1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
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  #5  
Old 07-09-2007, 12:44 PM
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Location: Houston, Texas
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Flushed with Selig - Kwik Solv. I buy it in gallon containers. Our shop air is dried to -40f dewpoint. Its dry. Flushed several times to get that damn dye out of the system. Then chased it with plenty of air. Flushed every component separately.

Both aux fans were running the correct direction. In fact I removed the plug off the temp sensor which makes them run at high speed. Fan clutch was working properly. AT one point I even had a squirrel cage blower sitting in front of the car adding more air flow.

I have proper gear - refrigerant recovery & recycling equipment and 2 vacuum pumps, electronic vacuum gauges - the works. Pulled a vacuum to 95 microns for 4 hours. Let it stand over night. Still good in the morning. Recharged with virgin R12.

I should have left in the original expansion valve. It worked really well. Its such a *tch to get at it I did the usual - replace while I am in there routine. I should have listened to my intuition.

The way I see it - its gota be the Ex valve. There is nothing else in the system that could cause the problem. Compressor is obviously good - what else is there? There is only really two components in the system - compressor and Ex valve. The rest is just tubing or plumbing. Not much to go wrong. I dont think the valve is bad, I think it is set wrong. I had considered cutting a slot in the adjuster so I could turn it after it is installed. But I didn't.

Oh well.
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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k

Last edited by dpetryk; 07-09-2007 at 12:52 PM.
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  #6  
Old 07-09-2007, 01:03 PM
dpetryk's Avatar
Electrons can do anything
 
Join Date: Sep 2001
Location: Houston, Texas
Posts: 1,072
I am now replacing the vacuum elements now. Maybe that will help.
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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k
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  #7  
Old 07-09-2007, 04:53 PM
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Bob G
 
Join Date: Dec 2002
Location: Long Beach ,California
Posts: 276
Question 92 300E needs Ac recharged

Can anyone recommend to me a good shop to charge the AC on my 1992 300E
the car has only 38,000 miles and is black on black too hot to drive in Los Angeles with out AC. Also my owners manual says R134 and R12 which is correct?
any recomendations would be appreciated.

bob Geco
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  #8  
Old 07-09-2007, 05:15 PM
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Location: AL
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There should be a label under the hood which specifies the refrigerant type and amount.

Also, look at the fittings. If there are small connectors with threads it uses R12. If it is a larger fitting with no threads on the outside, it uses R134A.
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  #9  
Old 07-10-2007, 02:48 AM
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Location: New Orleans LA
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Cooling problem

If there is too much oil in the system it will affect cooling and you should
take your readings at about 1500 rpm and those pressure reading are relative to the out side temp. and if you don't have good air flow over the
condenser the pressure will be up. with the system running and your gages on take a garden hose and run water across the condenser and watch your pressure's drop high side and low side

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