Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help




Go Back   PeachParts Mercedes ShopForum > Technical Information and Support > Tech Help

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 06-23-2002, 12:40 PM
Registered User
 
Join Date: Jul 2000
Location: New York, New York
Posts: 179
W124 Expansion Valve

Folks,

The next real problem is weak cold air from the AC. Last week I had it recharged to no avail. Nick, my independent, looked at it again today and claims that the problem is the expansion valve. He came to this conclusion by watching the pressure gage he connected and taping on the expansion valve with a large screw driver and seeing the pressure drop momentarily.

He was measuring from the Schrader valve on the cold side driver side by fender) and it was between 60 & 80lbs. He said he expected 40.

He says this is a four hour job, ouch. Does anyone have an opinion about this problem? Any one have some way to confirm his diagnoses? Or better yet, a trick to try and coax one more summer out of this valve?

I my search revealed a lot of scary evaporator discussions, but not much about the expansion valve (other than to replace it when you do the other stuff.)

Thanks,
__________________
-Mike
'87 300TD 304kmi (RIP)
'95 Toyota Camry Wagon 125kmi
Reply With Quote
  #2  
Old 06-23-2002, 01:36 PM
Moderator
 
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Well, here's hoping he is correct.

I would bet big odds against it though. Number one reason is that's not the way we see that expansion valve fail. To account for those pressures the expansion valve would have to allow a tremendous flow. I'm not sure the block type valve can do that. I can tell you that the last ten that I prayed were (that), weren't.

Unfortunately the more likely problem is the worse problem that system can endure. It sounds more like the pressures of a compressor running in the throughs of the "Black Death".

Try a valve as they are cheap. I would not do anything else until that diagnosis is complete. It other words, no flushes, no driers, etc. Plug in a new valve, examine the insides for contamination, see if the pressures are good and then do further maintenance if the diagnosis proves correct.
__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
Reply With Quote
  #3  
Old 06-23-2002, 06:18 PM
Registered User
 
Join Date: Jun 2000
Location: Plano, TX
Posts: 2,503
Four hours sounds a bit steep. I can have the expansion valve in & out of my 124 wagon in about 30 minutes - it just ain't that difficult a job. Of course, there's the matter of recovering the refrigerant first, vacuuming the system, and recharging - all will add time. But four hours sounds high to me.

How does the sight glass on the dryer look? If it has become opaque rather than clear, you may have a clue to the problem.

The most likely cause of the low side showing high pressure is a dying compressor. Is the high side pressure too low?
Reply With Quote
  #4  
Old 06-23-2002, 11:36 PM
Registered User
 
Join Date: Jul 2000
Location: New York, New York
Posts: 179
Steve,

Doesn't sound good. My Mec. didn't measure the highside pressure and I couldn't get a good look at the sight glass. So I can't report on that.

What I can say is that it worked better before he charged it. In fact I think my problem was do to the fact that the car was over heating and the compressor was shutting off while sitting in traffic.

Is there such a thing as over charging?

I searched the archives for this topic, but I found many references to "Steve's" disertation on the Black Death, but I didn't find it. Are you the Black Death Steve?

Thanks,
__________________
-Mike
'87 300TD 304kmi (RIP)
'95 Toyota Camry Wagon 125kmi
Reply With Quote
  #5  
Old 06-24-2002, 09:03 AM
Moderator
 
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
I may be big and ugly, but I'm not the black death.

The "black death" is a condition that occurs in primarily Nippondenso compressors (this especially includes the one's Ford builds under license). It is prevalent in these compressors because they use teflon coated pistons instead of piston rings. What makes the black death is not the black of the powdered aluminum in the mix. The death comes from the special characteristic that vaporized teflon adds to the slury of melted, gauled, aluminum, oil and refrigerant. The teflon bonds the stuff together in a solid at room temp. The stuff coats the whole system with something thats a little darker and very much like graphite. The big problem is the stuff in the condenser. When the system is flushed and repaired the condenser get hot during operation and the stuff goes liquid and gets back in motion.

Its about impossible to flush but I would not even consider flushing the condenser in such cases, just pitch it.
__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
Reply With Quote
  #6  
Old 06-25-2002, 01:51 AM
Mike Murrell's Avatar
Registered User
 
Join Date: Feb 2000
Posts: 2,351
If you believe what's presented in tech manuals...ie...."Automotive Air Conditioning Basic Service Training Manual" by Mastercool and what I think I've read here, it's possible the system is indeed overcharged.

There's a pressure-to-temperature relationship - refrigerant. Ideally, you want things close to but not quite at 32F in the evaporator. I'm not sure why the tech would be looking for 40lbs on the low side. That equates to 45F. Between 20-80 psi, temp. & pressure change together - 1 psi increase in pressure results in 1 degree F change in temp. Ideally, you'd want a low side pressure closer to about 30 psi. I find it odd that the high side was not checked at the same time?

Is the system cycling more often than when it was performing correctly? Overcharged systems cycle often and vents temps. are less than desireable.

As Steve Brothertom pointed out, your compressor could be sick and in this case, I'd expect to see low pressure on the high side.

Bottom line - tech didn't read both sides, so it's tough to say. In my opinion, you should have it reevaluated by someone else.
__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"
Reply With Quote
  #7  
Old 06-25-2002, 12:26 PM
Registered User
 
Join Date: Jul 2000
Location: New York, New York
Posts: 179
Steve & Mike,

Thanks for responding.

I agree that the system needs to be properly diagnosed and I won't be taking any action until it's been done by the book.

I did read in the ACC manual that high presure on the low side and low presure on the high side was indicative of expansion valve failure while equal presure was a compressor failure.

I am curious about the over charge, because the problem began after he charged it. I was thinking my AC needed checking because the compressor would cut out when the engine got hot. Now that the fan clutch is fixed that problem is gone. I wish I had left the AC alone.

As you all said it seems that the only way to know is to check the system properly on both sides. Am I correct in assuming that if both sides are above the correct presure that the system is over charged and the expansion valve may be OK?

Thanks,
__________________
-Mike
'87 300TD 304kmi (RIP)
'95 Toyota Camry Wagon 125kmi
Reply With Quote
  #8  
Old 06-25-2002, 04:44 PM
Registered User
 
Join Date: Dec 2001
Posts: 571
I'm curious. How did he measure just the low side pressure without measuring the high side pressu

Manifold gauges are designed to be connected in series so to speak - low side line on gauge connects to low side of system; high side line on gauge connects to high side of system.

Did he merely use one of those $3 tire gauge testers on the low side only?
Reply With Quote
  #9  
Old 06-25-2002, 04:55 PM
Registered User
 
Join Date: Jul 2000
Location: New York, New York
Posts: 179
Mike R.,

He used what appeared to be proper mainfold gages (two in tandem), but he only connected one side. The third end went to tank of R12. Which he opened at least once.

Is it possible that the readings are not correct unless they are both connected. Not sure if that makes sense to me.

Hmmm, are you saying that I could check the presure myself with a tire gage? How high will the high side be in lbs/in^2?

Thanks,
__________________
-Mike
'87 300TD 304kmi (RIP)
'95 Toyota Camry Wagon 125kmi
Reply With Quote
  #10  
Old 06-25-2002, 05:23 PM
Registered User
 
Join Date: Dec 2001
Posts: 571
Mike:

It simply makes no sense at all to me why a professional tech skilled in the ways of automotive air conditioning would only check the low side? This isn't really a good example, but to me it would sort of be like checking the tire pressure of the front/rear tires on the drivers side and not the passenger side.

I wouldn't give spit for one of those cheapy tire-gauge type a/c pressure testers. A/C pressures need to be checked with manifold gauges that are being handled by someone well-versed in their usage.

Based on what you've presented, I'd say you need to hire someone else to bring closure to this issue.

My 2 cents.
Reply With Quote
  #11  
Old 06-25-2002, 05:29 PM
Registered User
 
Join Date: Jul 2000
Location: New York, New York
Posts: 179
I think I agree.
__________________
-Mike
'87 300TD 304kmi (RIP)
'95 Toyota Camry Wagon 125kmi
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 09:21 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2011 Pelican Parts - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page