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  #31  
Old 06-04-2007, 08:19 AM
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Speaking of the overpressure sensor, specifically this one: http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=23O0HOZY623O0HP54S&year=1993&make=MB&model=400-E-001&category=R&part=A%2FC+Pressure+Switch, will it protect a system (compressor) if the a/c is ever overserviced. I guess 30 bar is about 435 PSI, so maybe that's too much for an old compressor to handle before it blows out.

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  #32  
Old 06-04-2007, 08:19 AM
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Regarding the WOT cutout of the A/C for a few minutes:

When this starts happening on a regular basis I replace the serpentine belt and install a new belt tensioner. This reduces it from a frequent occurrence to something that happens only occasionally.

Note that it is possible to improperly install the tensioner and damage the new part.
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  #33  
Old 06-04-2007, 09:19 AM
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Quote:
Originally Posted by emerydc8 View Post
Speaking of the overpressure sensor, specifically this one: http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=23O0HOZY623O0HP54S&year=1993&make=MB&model=400-E-001&category=R&part=A%2FC+Pressure+Switch, will it protect a system (compressor) if the a/c is ever overserviced. I guess 30 bar is about 435 PSI, so maybe that's too much for an old compressor to handle before it blows out.
Yes . to let comp run, the system needs 2 Bar [ that is so if you do not have any refrig, they do not want the comp to run]....and if the high side gets to 30b, it shuts down.
To get that high usually takes extreme ambients along with a nonworking aux fan/plugged condenser fins,et..but an overcharge could also trigger it..
..as a glazed/slipping belt can also interrupt the comp...Gauges are reguired for positive diagnosis..
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  #34  
Old 06-04-2007, 09:55 AM
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I was looking over Section 83-608 (Checking refrigeration capacity and suction/high pressure) and I saw that it calls for 2,000 RPM for ten minutes before measuring. Does anyone do this? It seems that 2,000 RPM without moving forward for ten minutes would create quite a bit of heat. I'll bet the aux fans would be on high by then.
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  #35  
Old 06-04-2007, 09:38 PM
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Funny you should mention the belt and tensioner. I was driving today and noticed the belt liked to chirp occasionally (only when the air is on). The belt has about 40-50K on it so it is probably time to do something with it anyway. As far as the tensioner goes, what is the typical lifespan on them? Seems like at 105K it might be time to replace it for good measure. Thoughts?

Bob
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  #36  
Old 06-04-2007, 10:51 PM
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I've noticed with a weak tesioner that if I let OFF the accellerator from WOT suddenly, the belt will squeak on DECELERATION and then the A/C will cut out for a while. A new belt and tensioner has fixed it for me consistently. If I use WOT and then let off gently it may not squeak and will usually not kill the A/C.

At 235k miles, I have replaced the tensioner at least twice and probably three times on my 92 400E and similarly on the 92 SL. I may be replacing it too often, but each time it fixes the A/C dropouts after using WOT.

My shop tells me if it ever squeaks it is probably the tensioner and not the belt. Of course, they don't recommend a new tensioner without a new belt to go with it. This shotgun fix seems all too un-scientific, but I cannot argue with success.

I've been reading Arthur's expert detailed posts on this. He seems quite knowledgeable has good information and may have other ideas. If I ever have a complex problem in my electronics I'd appreciate having his input.

Arthur: Any ideas on troubleshooting an intermittent ASR Limp-Home problem on my 92 SL?
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  #37  
Old 06-04-2007, 11:23 PM
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A most common problem with belt slipage and tensioner longevity is guys take the bottom engine cowling panel off thinking they are improving airflow for the engine .. It not only does not work as airflow is channeled with the cowling and removal also lets water and road rash wear both the belt and tensioner. Belt slipage is very common in the rain w/panel removed.
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  #38  
Old 06-04-2007, 11:26 PM
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You can get codes for asr diagnostics, but most common intermittent problems are caused by unequal tire sizing/pressure or faulty brake light switch.
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  #39  
Old 06-05-2007, 04:44 AM
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I agree about the water and dust! Here's a story of an experience with just that!

A couple years ago we had a torrential summer rain storm in Atlanta and I got caught out in it trying to get home from work. I had to drive through streets in my 400E that were flowing with water channeled between the curbs.

I had a heck of a time trying to keep the windshield clear from the INSIDE because the A/C kept cutting out since I could not keep the belt dry. I was wiping the windshield with paper napkins, running the defroster until I was sweating and restarting the engine every couple of minutes. It was so hot inside the car that I had to open the windows a bit to breathe!

Looking back it was pretty funny, but what an experience! No, I had not removed the bottom engine cover. My tensioner was getting old and it was just so wet that I could not keep the belt dry.

Yeah, removing the bottom cover is not wise and I also don't recommend using dust shields in the wheels. I have temporarily lost my brakes due to overheating caused by those dangerous little inserts. It is a scary feeling to press the brakes and feel that nothing is happening when you need them most!

I don't want to hijack this thread to pursue on ASR problem, but it is very intermittent and my shop says my 92 SL loses the codes if I turn the switch off. Is this true on a 92 or do they just not have the right code reader or something? Oh, the brake light switch and OVP relay were changed early on.
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  #40  
Old 06-05-2007, 10:41 AM
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Pin #7. page 47

res://ieframe.dll/navcancl.htm#http://www.geocities.com/MotorCity/Downs/1039/mercedes/cs1000_mb.pdf

As I mentiomed , check tire sizing..the ASR EA module looks at/compares all 4 tire circumferences/rpm...

Last edited by Arthur Dalton; 06-05-2007 at 11:18 AM.
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  #41  
Old 06-05-2007, 11:26 AM
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You are right about the squealing on deceleration. The times I have noticed it has been when it shifts to the next gear and the RPM drop quickly. I think I am keeping UPS in business ordering all these parts! One belt and Tensioner please
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  #42  
Old 06-05-2007, 12:23 PM
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Ok, it sounds like you will do the tensioner yourself, so be careful to install it with the proper tension and observe which way the flat tensioner arm is turned. Watch out for a spacer that may be behind the tensioner. It may fall unexpectedly and not give you a chance to see from whence it came.

It is not a difficult job, but a picky one! There are little notches on the arm and a removeable plastic pointer that indicates how much tension you have applied.

I don't have the official tension procedure but will tell you what I use. If someone has the official word please post it. There are other posts about this on this site so you might want to do a search.

Here is how I recall that I did it: The marks are evenly spaced except for the first one. I align the pointer to that one while it is relaxed and install the tensioner leaving the main bolt slightly loose. I then tighten the tensioning rod until the plastic pointer moves to about the center of the remaining notches. I think that is 2-3 notches over. Then once adjusted, tighten the center bolt and you are done. Too little tension and the belt will slip. Too much tension and you will rip the rubber bushing and render the new tensioner useless. It appears that the tension is create by stretching (rotationally) the rubber bushing in the center.

Good luck!
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  #43  
Old 06-05-2007, 12:25 PM
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Belts loose their friction drive quality as they age and 60K is a good time to change one..I put the new one on and the old one [ which is still a good back-up] in the Trunk, just in case..Cheap insurance.
Same goes for hoses..don't throw that old radiator hose out..put it in "da Trunk " when you put the new one on.
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  #44  
Old 06-05-2007, 12:37 PM
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I thought that this switch "http://catalog.worldpac.com/mercedes...ressure+Switch" was only a Low Pressure switch - switching the compressor off in the event of ac gas being lost to the atmosphere, it has nothing to do with high pressures that being the job of the reg or green HP switch
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  #45  
Old 06-05-2007, 12:54 PM
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Your link does not work, but most all comp low refrig [30psi] are a bi/sw that also cuts out comp at extreme highside pressures.. like this one

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=23O0HOZY623O0HP54S&year=1993&make=MB&model=400-E-001&category=R&part=A%2FC+Pressure+Switch

The high side pressure sw for aux fan [ mis-labeled temp sw]has nothing to do with comp cut-out, it only controls fan cut-in/out.

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