Rennlist Discussion Forums   classifieds | membership | rennlist | photo album    
sponsors | upload photo | chat    
 
Go Back   Rennlist Discussion Forums > Water Cooled Technical Discussion Areas > 928 Forum
Sign in using an external account
Register Forgot Password?
Search


This Rennlist Forum is sponsored by      ....dedicated to Your Porsche 928

Reply
 
Thread Tools Search this Thread
Old 06-30-2004, 12:09 AM   #1
JPTL
Addict
Rennlist Member
 
JPTL's Avatar
 
Join Date: Aug 2002
Location: Potomac, MD
Posts: 1,889
Default A/C Leak on Low Side...What to look for?

At the beginning of last A/C season, I did a 134a conversion (adapter valves, some O-rings, rec/drier, oil). It got me through the summer fine, but I've lost all of my freon over the winter. I took it to the A/C specialist who originally did the conversion, and he dialed in some pressure on the high & low sides. Pressure dropped pretty rapidly for both. After finding/replacing a bad O ring at the pressure switch next to the drier, we still noticed a pressure leak on the low side. Since the belly pan was on, the lines weren't very accessible without getting the car up on ramps & removing the pan, he turfed the leak detection to me. I'm in the process of getting hold of a dye light (dye is in the system).
The A/C guy suggested that I trace the low side hoses to each connector, starting with the compressor...and go back.
Are there any connections that are prone to leaking on the low side? How many connections/points of possible failure am I looking at before getting to the firewall & going inside?
As far as the rear A/C's concerned, are there any accessible couplings that I should check out from under the car? Any connections prone to leaking back there?
To remove this ad, register today or login if you already are registered!

__________________
J.P.
'91 GT
Black/Classic Gray
'88 S4 5 Speed/LSD
Silver/Cancan over Black
'07 Triumph Sprint ST ABS
The Official US Frenzy Site

There is a very fine line between "hobby" and "mental illness."
-Dave Barry
JPTL is offline   Reply With Quote
Old 06-30-2004, 12:13 AM   #2
ViribusUnits
Super User
 
ViribusUnits's Avatar
 
Join Date: Aug 2002
Location: South Texas
Posts: 9,011
Default

How can you trace it to the low side?

It's all one system, and the gas will go between the two sides freely. the gas can really flow eighter diriction through the expanshion valve.

There are no connections inside the dash. From the dash to the compressor, there are 4 connections. They're all o-ring type connections.

From the dash to the compressor for the high side there are 6 connections.

Good luck.

I forgot all aobut the rear air. Sorry about that.

Last edited by ViribusUnits; 06-30-2004 at 04:14 AM.
ViribusUnits is offline   Reply With Quote
Old 06-30-2004, 12:22 AM   #3
Steve J.
Addict
Rennlist Member

 
Steve J.'s Avatar
 
Join Date: Jul 2001
Location: Irving, TX
Posts: 1,327
Default

There are connections for the rear AC under the car. The integrity of the system is as good as the weakest joint. Every o-ring should be replaced IMO.
Steve J. is offline   Reply With Quote
Old 06-30-2004, 12:47 AM   #4
fst951
User
 
Join Date: Apr 2004
Location: Snyders Mill, Utah
Posts: 780
Default

Steve is right, just flush the whole system and replace all the o-rings at a bare minimum.

Good luck!
fst951 is offline   Reply With Quote
Old 06-30-2004, 01:26 AM   #5
JPTL
Addict
Rennlist Member
 
JPTL's Avatar
 
Join Date: Aug 2002
Location: Potomac, MD
Posts: 1,889
Default

Quote:
How can you trace it to the low side?
The A/C guy had two gauges connected to what he explained as the high (pressure) side - by the drier; and the low side - other side of the radiator by the pass. fender.
His explanation was that the high side provides the pressure, and the low side is a like a vacuum. I listened to him, and assumed that he knows what he's talking about since he's been doing automotive A/C for 30+ years.
After replacing the O-ring on what he indicated was the high side, the gauge hooked up to that 'side' showed no pressure loss. The second gauge, hooked up to the 'low side' showed a pressure loss. I got the impression from him that the problem was likely in the low pressure line(s).
I agree with the consensus. I plan to take my time and replace all the O-rings. However, I'd like to know the culprit via a UV light, since it may not be O-rings at all.
__________________
J.P.
'91 GT
Black/Classic Gray
'88 S4 5 Speed/LSD
Silver/Cancan over Black
'07 Triumph Sprint ST ABS
The Official US Frenzy Site

There is a very fine line between "hobby" and "mental illness."
-Dave Barry
JPTL is offline   Reply With Quote
Old 06-30-2004, 01:55 AM   #6
Wild Bill
Addict
Rennlist Member

 
Wild Bill's Avatar
 
Join Date: Jul 2003
Location: Houston, Texas
Posts: 396
Default

I just got through dropping my compressor... again, after replacing the receiver drier, expansion valve and all the o-rings. Vac'd, recharged and put the UV dye in the system, which revealed a huge leak in the low side hose to the compressor. Leak appears to be crack in the hard line where it goes into the crimped (swaged - sp?) fitting at the top near the low side port. The UV dye made it stand out like a sore thumb... Find a lamp and you should be able to find the leak.

If I take the hose in to have barrier hose installed, should the A/C component rebuilder be able to fix the crack and pressure test it? I don't want to have to do this job again.

Bill
Still waiting for the thrill of the chill!
Wild Bill is offline   Reply With Quote
Old 06-30-2004, 02:12 AM   #7
mpesik
Banned
 
mpesik's Avatar
 
Join Date: Oct 2003
Location: on a huge ball
Posts: 7,850
Default

O.T- Mr. JPTL. I've asked you before and will forever ,until you give me an answere. WHAT KIND OF WAX or POLISH DO YOU USE !!! Something they used on HUBBLES mirror?JPTL or JPL. Which one are you? Mike?
mpesik is offline   Reply With Quote
Old 06-30-2004, 02:19 AM   #8
borland
Super User
 
Join Date: Aug 2003
Location: Camarillo, CA, USA
Posts: 2,258
Default

Replacing all the o-rings is not an easy task. If you have rear a/c, there are a total of 22 mechanical joints on the car, each with an o-ring, plus 5 hoses. Each hose has two ends that are crimped on fittings. So there are 32 most likely places that a leak can occur. Plus, the compressor has additional o-rings and shaft seals.

Less likely, but possible are leaks thru the hard lines (tubing) and system components.

UV lamp, soap bubble, and halogen leak tester are the typical method/tools for performing leak checks. But you can also spot leaks by seeing signs of oil.

Assuming you still have a partial refrigerant charge, the low pressure lines can be checked without running the engine or a/c. The high pressure side is normally checked while runing the compressor, which brings up the pressure substantially on the high side, but drops the pressure on the low side.
borland is offline   Reply With Quote
Old 06-30-2004, 02:32 AM   #9
borland
Super User
 
Join Date: Aug 2003
Location: Camarillo, CA, USA
Posts: 2,258
Default

Bill,

They might be able to braze repair the fitting, but the rebuilder should probably replace the aluminum fitting. The replacement fitting is readily available.

The replacement part is a standard "Beadlock, 45 degree, female o-ring, fitting size 10, hose size 12".

http://www.atcoproductsinc.com/catalog/
borland is offline   Reply With Quote
Old 06-30-2004, 04:13 AM   #10
ViribusUnits
Super User
 
ViribusUnits's Avatar
 
Join Date: Aug 2002
Location: South Texas
Posts: 9,011
Default

That doesn't make any sence.

The a/c system is a sealed system, in which the freon flows around and around. The freon moves through the expanshion valve from the high side, to the low side. If the a/c compressor is off, the freon will rapidly flow untill both sides are at the same pressure. If they are not, something is wrong. With the compressor on, (pretty much the correct way to check system pressures) the freon is constantly going around and around. If the system has a leak, the expanshion valve closes up slightly, resulting in a bit higher restriction. This keeps the high sides pressure up, but lowers the low sides. This is why a leak typicaly shows up on the low sides pressure, untill the freon is really low. That doesn't mean the system has a leak form the low side, just that there is a leak. At least thats been my experence.

Eighter you miss understood the a/c guy, or you need to find a new a/c guy.
ViribusUnits is offline   Reply With Quote
Old 06-30-2004, 01:38 PM   #11
dr bob
The Doctor is IN
Lifetime Rennlist
Member
 
dr bob's Avatar
 
Join Date: Oct 2001
Location: Bend, Oregon
Posts: 11,612
Default

I'm with VBU-- I'm not certain how you decide that a leak is in the low side or high side, unless you actually identify the leak. They are, after all, connected in a couple places. Watching the gauges with the system running, and determining that the leak is on the low side because that gauge moves lower? What that means is that the evaporator is cooling off. If the guy has been making that same assumption for 30 years, well... Good for him.

Meanwhile, my hit-list of common "I forgot to fix these things when I did the
conversion" items includes:

O-rings at the rear expansion valve.
O-rings at the front expansion valve.
Fittings and seals at the rear AC solenoid valve under the passenger seat.
tube fittings at the rear evaporator (described by Wally in a separate post)
O-rings where the hose connectors attach to the compressor housing (this one got me...)
O-rings where the lines for the rear air branch off just under the fuse panel forward of the firewall.
Bulkhead fittings where the rear AC lines pass up through the floor under
the passenger seat.


Many "conversions" are done by changing the o-rings at the hose ends and the drier connections, and changing the oil. There are at least a dozen other places where you can have leaks at fittings and o-rings, obviously. If your conversion was done at medium speed, sort of half-fast, you'll progressively discover those other places. I worked at a reasonable pace and still spent the best part of a day getting all the potential leak spots re-O-ringed.

Found those last four o-rings a couple days later, after the new oil had a
chance to soften the old rings. These are the ones where the little
fittings that accept the hoses actually mate with the compressor. Two allen
bolts attach each fitting to the compressor, two O-rings under each fitting.


I really found the electronic leak detector to be the best method. The
dye-and-hunt method assumes that you have easy access to the places where the system might leak. I guess you could say that the 928 has that access, but not unil a good portion of the pass side interior is pulled out and the rear console uncovered. Meanwhile, the sniffer probe is at the end of a long flex section that allows you to poke it into places without a complete disassembly. It detects leaks down to the few-grams-per-year level, something the dye-and-hunt method won't ever match. If you are in the Los Angeles area, you are welcome to us the one I have.


Hope this helps!


dr bob
__________________
'89 S4 Auto, black

Rennlist Member
928OC Charter Member #81
SoCal 928 Co-Founder #3
PCA SGVR Member
---------------------
Free advice and shared experience, with absolutely no relationship to your real-world conditions. No warranty of any kind expressed or implied. Use at your own risk.
dr bob is online now   Reply With Quote
Old 06-30-2004, 04:03 PM   #12
Garth S
Addict
Rennlist Member
 
Garth S's Avatar
 
Join Date: Oct 2003
Location: Nova Scotia
Posts: 7,069
Default

Quote:
Originally posted by mpesik
O.T- Mr. JPTL. I've asked you before and will forever ,until you give me an answere. WHAT KIND OF WAX or POLISH DO YOU USE !!! Something they used on HUBBLES mirror?JPTL or JPL. Which one are you? Mike?
Mr Mike - to a (too) casual observer, it looks very much like TREE WAX.

Re. the A/C, in a sealed, closed loop system, a leak is a leak is a leak - another vote that says the whole system is suspect.
__________________
'96 993 C4S Midnight blue , Bilstein HD, M030 bars & turbo springs, FPB, SSK, wide ovals w. LPMM, 8"/11" 'hollows',or RS-GT's Schnell brace
'80 928 Copper brown 5-sp, Konis, euro S springs/brakes, CS wheels, S4 wing
Garth S is offline   Reply With Quote
Old 06-30-2004, 05:00 PM   #13
JPTL
Addict
Rennlist Member
 
JPTL's Avatar
 
Join Date: Aug 2002
Location: Potomac, MD
Posts: 1,889
Default

Well, thanks for the replies. They're coming from people who certainly know considerably more about auto A/C and exactly what's under my car. The way the guy tested it was with compressed air (or gas...I'm not sure) & an empty system...not with the system running. I don't know if that makes any difference in being able to isolate between high & low....doesn't look like that's the the consensus in this thread. What's clear to me, is that I need to isolate the leak if possible, and regardless of whether or not the leak can be isolated to the high or low side, I'm in for some serious O-ringing...whether I find the specific source of the leak or not. Sitting here in my comfortable highback chair speculating about what could be causing the leak isn't gonna cut it. However I am going to be crawling under the car with a much better education about what to look for, and how far I should go to prevent having to crawl back under in a couple of months, thanks to you guys.
Dr. Bob, I appreciate the offer to use the sniffer. I wish I had such a generous offer here in MD. That would surely do the trick. I'll have to make do with a UV light.
Mike, it was a particularly shiny day for my car. I just wish I'd taken the pic. in higher resolution. Every 3 waxings, I use 3M Handglaze which seems to be liked by most on this list; followed by One Grand Blitz Carnuba, which seems to be a debatable choice by most on this list. Take a look at this thread:
http://forums.rennlist.com/rennforum...hreadid=140672
Thanks again for the helpful posts.
__________________
J.P.
'91 GT
Black/Classic Gray
'88 S4 5 Speed/LSD
Silver/Cancan over Black
'07 Triumph Sprint ST ABS
The Official US Frenzy Site

There is a very fine line between "hobby" and "mental illness."
-Dave Barry
JPTL is offline   Reply With Quote
Old 06-30-2004, 09:37 PM   #14
mpesik
Banned
 
mpesik's Avatar
 
Join Date: Oct 2003
Location: on a huge ball
Posts: 7,850
Default

Thankyou Mr. Garth. And then thanks Mr.JPL. Mike
mpesik is offline   Reply With Quote
Old 06-30-2004, 09:37 PM
Rennlist



Paid Advertisement
Reply

Tags
ac, car, connections, cruiser, find, finding, high, leak, leaks, light, low, port, pt, rear, side, type

Thread Tools Search this Thread
Search this Thread:

Advanced Search

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 Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Forum Jump


All times are GMT -3. The time now is 12:25 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
SEO by vBSEO 3.6.1
Copyright ę 1998 - 2007 Rennlist.com

Advertise on Rennlist - Privacy Statement - Terms of Service - Jobs