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 08-13-2002, 04:36 PM
Registered User
 
Join Date: Dec 2000
Location: Fairfax County, Virginia
Posts: 856
What should "low side" of refrigerant cycle be?

Have had my 350 SDL for about 2.5 years ... has always cooled well. Noticed recently that it is cycling more in and out of cooling ... I figured was due to natural loss of R-12 ... I understand this can happen from 0.1 to 0.25 per year in even well sealed systems on cars.

So, I put on low side hose to put a can of R-12 in ... I ended up with about 38 inches on the low side after starting at about 30. Air is a bit colder, but more importantly, the cycling has been signficantly reduced.

As you can probably tell, it has been many years since I worked on auto a/c systems ... did I do this right? Was my diagnosis correct re the loss of coolant causing the cycling in the absence of other problems?
__________________
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
Reply With Quote
  #2  
Old 08-13-2002, 05:06 PM
mikemover's Avatar
All-seeing, all-knowing.
 
Join Date: Aug 2001
Location: Atlanta, GA
Posts: 5,514
I think you're on the right track...the cycling is the result of the compressor protecting itself...If there's not enough R12, it turns itself off to prevent overheating of the compressor,and/or pumping air/moisture/other crap through the system.

A leak will only get larger over time, so I'd have it sniffed out and repaired ASAP.


Mike
__________________
_____
1979 300 SD
350,000 miles
_____
1982 300D-gone---sold to a buddy
_____
1985 300TD
270,000 miles
_____
1994 E320
not my favorite, but the wife wanted it

www.myspace.com/mikemover
www.myspace.com/openskystudio
www.myspace.com/speedxband
www.myspace.com/openskyseparators
www.myspace.com/doubledrivemusic
Reply With Quote
  #3  
Old 08-13-2002, 05:22 PM
Registered User
 
Join Date: Dec 2000
Location: Fairfax County, Virginia
Posts: 856
mikemover,

Thanks. To my knowledge this is the first F-12 ever added! Is there a chance I don't really have a "leak" in the classic sense? Car is 12 years old, now.
__________________
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
Reply With Quote
  #4  
Old 08-13-2002, 05:37 PM
Registered User
 
Join Date: Jun 2000
Location: Plano, TX
Posts: 2,503
Can you explain in more detail what you mean by "cycling in an out of cooling?" It isn't clear to me what you are trying to say...
Reply With Quote
  #5  
Old 08-13-2002, 05:44 PM
mikemover's Avatar
All-seeing, all-knowing.
 
Join Date: Aug 2001
Location: Atlanta, GA
Posts: 5,514
jcyuhn,

He means that the compressor is cycling on and off on its own...which is what it's supposed to do, progressively, as the refridgerant level gets lower and lower.

stephenson,

12 years without adding any R12 is pretty damn good, but like I said...small leaks become big leaks eventually, and R12 is not cheap!


Mike
__________________
_____
1979 300 SD
350,000 miles
_____
1982 300D-gone---sold to a buddy
_____
1985 300TD
270,000 miles
_____
1994 E320
not my favorite, but the wife wanted it

www.myspace.com/mikemover
www.myspace.com/openskystudio
www.myspace.com/speedxband
www.myspace.com/openskyseparators
www.myspace.com/doubledrivemusic
Reply With Quote
  #6  
Old 08-13-2002, 05:50 PM
mikemover's Avatar
All-seeing, all-knowing.
 
Join Date: Aug 2001
Location: Atlanta, GA
Posts: 5,514
If you top it off, and it continues to cool and operate normally, then I'm sure the leak is VERY small, so I guess I would weigh the cost of finding and fixing the leak vs. the cost of topping off the R12 and compressor oil periodically. The leak WILL grow over time...it's just a matter of how quickly.

There is also this issue: It is "technically" illegal to add R12 to a system that is known to have a leak. Most shops would not do it for you. I think the whole R12 thing is bulls**t anyway, but just in case you weren't aware....


Mike
__________________
_____
1979 300 SD
350,000 miles
_____
1982 300D-gone---sold to a buddy
_____
1985 300TD
270,000 miles
_____
1994 E320
not my favorite, but the wife wanted it

www.myspace.com/mikemover
www.myspace.com/openskystudio
www.myspace.com/speedxband
www.myspace.com/openskyseparators
www.myspace.com/doubledrivemusic
Reply With Quote
  #7  
Old 08-13-2002, 06:22 PM
Registered User
 
Join Date: Dec 2000
Location: Fairfax County, Virginia
Posts: 856
mikemover,

Understand. That is kind of at the crux of my point. Is one pound every 12 years a leak?
__________________
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
Reply With Quote
  #8  
Old 08-13-2002, 06:41 PM
mikemover's Avatar
All-seeing, all-knowing.
 
Join Date: Aug 2001
Location: Atlanta, GA
Posts: 5,514
Good point...if you can go another 8-12 years before adding another pound, then I'd say don't sweat it!

Mike
__________________
_____
1979 300 SD
350,000 miles
_____
1982 300D-gone---sold to a buddy
_____
1985 300TD
270,000 miles
_____
1994 E320
not my favorite, but the wife wanted it

www.myspace.com/mikemover
www.myspace.com/openskystudio
www.myspace.com/speedxband
www.myspace.com/openskyseparators
www.myspace.com/doubledrivemusic
Reply With Quote
  #9  
Old 08-13-2002, 07:03 PM
Registered User
 
Join Date: Dec 2000
Location: AL
Posts: 1,219
Quote:
Originally posted by mikemover
jcyuhn,

He means that the compressor is cycling on and off on its own...which is what it's supposed to do, progressively, as the refridgerant level gets lower and lower.
I believe the compressor will actually run MORE as the coolant level drops. When properly charged, the compressor cycles on and off - it's determined by the cooling needs...and to prevent freeze-up of the evaporator.

There is, however, a pressure switch which will shut down the compressor altogether if the coolant pressure (level) falls too low.
Reply With Quote
  #10  
Old 08-14-2002, 05:40 AM
LarryBible
Guest
 
Posts: n/a
I learned in taking my 609 certification test that topping off a known leaking R12 system is NOT against the law. Many shops tell people this to get them to do more major work or converting. THEY are violating the law in telling you this. The Better Business Bureau does not like them telling you this.

It is possible that this was just the normal leaking of refrigerant that happens over time. A minute amount of refrigerant leaks from all systems.

It is also possible that it is a more major leak. If one can topped it off and it is okay, you need to just wait and see. If you indeed decide to look for and repair the leak. Put in some UV dye, wait a week or two and use a black light and yellow glasses to look for a leak. If you find one, take the car to an a/c shop and have them recover the R12 before repairing the leak. They will even pay you for it if it is not contaminated.

You are DEFINITELY on the right track.

Good luck,
Reply With Quote
  #11  
Old 08-14-2002, 12:16 PM
mikemover's Avatar
All-seeing, all-knowing.
 
Join Date: Aug 2001
Location: Atlanta, GA
Posts: 5,514
Hey, Larry! Long-time-no-talk! Thanks for setting the record straight on the legality of that...I've obviously been misinformed a couple of times about that.

brewtoo,

I think I'm correct about the compressor...I had the same problem and experience with my 300SD...The more R12 I lost, the more often the compressor would cycle on and off, until finally it would not come on at all. I had the leaking hose replaced, charged it up, and now it's fine.

mike
__________________
_____
1979 300 SD
350,000 miles
_____
1982 300D-gone---sold to a buddy
_____
1985 300TD
270,000 miles
_____
1994 E320
not my favorite, but the wife wanted it

www.myspace.com/mikemover
www.myspace.com/openskystudio
www.myspace.com/speedxband
www.myspace.com/openskyseparators
www.myspace.com/doubledrivemusic
Reply With Quote
  #12  
Old 08-14-2002, 01:17 PM
engatwork's Avatar
busy
 
Join Date: May 2000
Location: Soperton, Ga. USA
Posts: 11,776
Mike - I take it the 4 cans r12 was enough to get you going and you are riding in a/c comfort now?
__________________
Jim
Reply With Quote
  #13  
Old 08-14-2002, 01:20 PM
Registered User
 
Join Date: Aug 2001
Location: secret
Posts: 3,044
But to answer the question..

Approx. 35 PSI.
Reply With Quote
  #14  
Old 08-14-2002, 01:49 PM
mikemover's Avatar
All-seeing, all-knowing.
 
Join Date: Aug 2001
Location: Atlanta, GA
Posts: 5,514
Jim,

45 degrees F at the center vents! My low pressure hose had a leak...had it rebuilt, charged it up, and it's working like new!

Thanks a MILLION!
See you next month. I'll e-mail you soon and we'll work out an exact date, etc.

Mike
__________________
_____
1979 300 SD
350,000 miles
_____
1982 300D-gone---sold to a buddy
_____
1985 300TD
270,000 miles
_____
1994 E320
not my favorite, but the wife wanted it

www.myspace.com/mikemover
www.myspace.com/openskystudio
www.myspace.com/speedxband
www.myspace.com/openskyseparators
www.myspace.com/doubledrivemusic
Reply With Quote
  #15  
Old 08-14-2002, 05:52 PM
csnow's Avatar
Registered User
 
Join Date: May 2002
Location: Mass
Posts: 1,127
Quote:
Originally posted by stephenson
Is one pound every 12 years a leak?
One pound every 12 years is really good results, and certainly not a leak. Auto systems are inherently leaky, unlike many stationary systems, which are sealed tighter.
__________________
1986 300E 5-Speed 240k mi.
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 12:17 AM.


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