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-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 08-09-2015, 03:35 PM
slow poke
 
Join Date: Jun 2011
Posts: 60
A/C blow off valve

83 300d with an r4. Charged with dura cool and was cooling fine for about ten minutes. Then something by the compressor let loose and dropped about 15 psi out if the system. Loud whistle sound. Is this compressor equipped with a "blow off valve" I am not very familiar with ac systems and may have over filled. Compressor still comes on but sight glass is cloudy now.

Reply With Quote
  #2  
Old 08-09-2015, 03:52 PM
Registered User
 
Join Date: Aug 2010
Location: Sacramento, CA
Posts: 2,953
You should have charged w/ two 6 oz cans. If you used 3 cans, that might have over-filled. I just cleaned and re-installed the R4 in my 1984 300D. There is a cir-clipped disk, that I assume has a spring-loaded relief valve (PRV) behind it, so sounds like your hypothesis is valid. In my other 300D, I put a Sanden w/ "GM Pad" head (to fit car's hoses) and added a screw-in PRV.

Don't go by the sight-glass. That is for R-12 and only a sanity check for at that. Judge by the pressures. I usually see 70 - 90 psig on the low-side w/ engine off and equilibrated, depending on outside air temp (say 80 - 105 F). With Duracool (HC), I usually see 120 - 190 psig high-side when compressor is running, again depends on outside temp.

Also, insure your electric radiator fan comes on when idling. If not, the condenser outlet gets almost too hot to touch and your AC won't cool well. The temp switch on the filter/drier often gets erratic. You can swap it without breaking into the system, and they are inexpensive here on Peach Parts. I tested 3 and all switched on @ ~83 F (found one was erratic). Alternative is do RollGuy's "relay mod. so always on w/ compressor".
__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans
Reply With Quote
  #3  
Old 08-09-2015, 04:06 PM
Registered User
 
Join Date: Sep 2001
Location: central Texas
Posts: 17,281
Quote:
Originally Posted by BillGrissom View Post
.....Don't go by the sight-glass. That is for R-12 and only a sanity check for at that. Judge by the pressures. .....
The FSM Rejects the use of the sight glass even for R12..... there are times they warn... that even totally full the sight glass will show bubbles... causing one to over fill if using that as your indicator.... about the worst thing you can do with an AC system as it works on the difference in pressure between the high and low sides...
Reply With Quote
  #4  
Old 08-09-2015, 08:15 PM
slow poke
 
Join Date: Jun 2011
Posts: 60
I have the electric fan on a switch and turn it on manually. It's working. I guess I overdid it with the freon. What I am wondering is if there was indeed a pressure relief valve that let off some pressure, is it something that is designed to shut back off so I can pull a vacuum and recharge without replacing it.
Reply With Quote
  #5  
Old 08-10-2015, 11:35 AM
Registered User
 
Join Date: Jan 2015
Location: northern IL
Posts: 267
R4 pressure relief valve

typical R4 (removed from a W126/300SD)

Reply With Quote
  #6  
Old 08-10-2015, 11:41 AM
Registered User
 
Join Date: Sep 2001
Location: central Texas
Posts: 17,281
There is the valve shown in the picture....
but I do not think any car has a valve which reseals...to the extent you could continue using the AC without causing problems.... my 95 Lincoln blew a valve like that ...not on the compressor... when the front fans stopped working... protected the compressor.... but it had to be replaced with a used one from a salvage yard because a new one was not still available.... and it did not reseal...
Reply With Quote
  #7  
Old 08-10-2015, 11:56 AM
Registered User
 
Join Date: Jan 2015
Location: northern IL
Posts: 267
Its a roll of the dice. I've had 'em seal up after a release, and I've had leakers. They are designed to close after an overpressure event, but corrosion can occur - that's the game changer. Also, the spring progressively weakens with age, exercise and corrosion so it may pop at lower pressure than when new.
Reply With Quote
  #8  
Old 08-10-2015, 01:37 PM
slow poke
 
Join Date: Jun 2011
Posts: 60
Quote:
Originally Posted by Charlie Foxtrot View Post
Its a roll of the dice. I've had 'em seal up after a release, and I've had leakers. They are designed to close after an overpressure event, but corrosion can occur - that's the game changer. Also, the spring progressively weakens with age, exercise and corrosion so it may pop at lower pressure than when new.
Thanks for the info. I have little to no money in the system and am planning on a Saden upgrade for next summer, so rolling the dice it is. Lets hope for the best.
Reply With Quote
  #9  
Old 08-10-2015, 02:17 PM
Registered User
 
Join Date: Jan 2015
Location: northern IL
Posts: 267
Is there anything still in the system? (Any pressure?) If yes, it's holding. If no, try pushing some N2 into the system and see if it leaks. If it leaks, take a 5/8ths deep thin wall socket (and rachet wrench) to the boneyard and collect a few. Look for mid 70-80-90's chevies, buicks, pontiacs V8s - they all used the same compressor (R4) and the compressor is mounted up high on the front of the engine - easy to get to it. Watch out & protect your eyes & fingers - if the system is charged, the release of refrigerant could freeze your flesh! Be carefull! Good luck!
Reply With Quote
  #10  
Old 08-10-2015, 03:06 PM
Registered User
 
Join Date: Aug 2010
Location: Sacramento, CA
Posts: 2,953
Thanks for the photo Charlie. I was wrong. I was referring to the lower-left port on a slanted surface. It is a disk held by a circlip. Don't know what is behind it.

Good that your PRV popped. I had the AC clutch smoke in 2 cars (one my 1985 300D), both on a very hot day. Both have an electric pressure switch, but as the clutches and compressors age, seems it can slip before that trips, and once it slips there is no turning back - gets hot real fast, slings molten plastic, ...
__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans
Reply With Quote
  #11  
Old 08-11-2015, 11:43 AM
rrgrassi's Avatar
mmmmmm Diesel...
 
Join Date: Jun 2006
Location: Royse City Tx
Posts: 5,122
My Hancock compressor locked like that with too high of pressure on a hot day at idle. Clutch smoked, but that appeard to be it, until a week later and the pulley bearing started grinding. That was not a fun replacement. Ever since I switched to Duracool, that problem went away. Car can idle on a hot day and compressor keeps spinning.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

06 VW Jetta TDI 133K miles-replaced the other '06 that quit after 300k miles. (did not catch the bad cam in time)

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 195K

90 Dodge D250 5.9 Cummins/5 speed. 400K
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 06:42 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2022, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page