possible leak on high pressure side of AC - PeachParts Mercedes-Benz Forum

ambush276 · #1 06-12-2016, 06:55 PM

So it took a couple of weekends but i finally got my entire system flushed, new expansion valve, new compressor, new belt, new drier, new a/c fridge temp switch, new a/c pressure switch, new seals everywhere. I finally got it all hooked up to the vacuum machine and did a test today. I pulled vacuum for an hour and then closed the valves on the gauges for an hr to see what the results were. Here they are

The low pressure side (blue) looks completely fine after the 2 hour test, but the high pressure (red) it is tough to tell. I checked the seals at the compressor and they seem very tight... the next question is... where else could it go wrong. The schraeder valve on the high side looks worn but it looks like it will be a b**** to change that out. Maybe that is somewhat normal for the high side but i wanted to see what other peoples opinions' were before i started to add the stop leak and refrigerant into the system.

car is an '82 240d.

Thanks all!

dkveuro · #2 06-12-2016, 07:16 PM

Did you zero your gauges ? You'll never pull a pure vacuum. Still some oil/moisture in system boiling off ?

FYI: holding a vacuum does not always mean it will hold pressure.

If you add Stop Leak or a system sealer you will ruin your gauge set.

.

leathermang · #3 06-12-2016, 08:40 PM

Vstech and I have been saying in plain English for a while that pulling a vacuum is not a leak test...
Why don't you go to the local welding store and rent a can of nitrogen for a month I think I said this in a pm already...
I also think that there is a TOOL for changing out the Schraeder Valve without removing the refrigerant .. that is listed in the archives and possibly in the AC thread in my signature..
NO ONE that I know of suggests putting ' stop leak' into an AC system...
Did you use the correct color of nylog when putting the system together ?

ambush276 · #4 06-13-2016, 12:03 AM

i used nylog blue. Well.. if it's not holding vacuum.. no point is trying to hold pressure? Need to fix the vacuum leak first before applying pressure.

I will avoid putting stop leak in the system as well if it is suggested.

ah-kay · #5 06-13-2016, 12:22 AM

This is my experience with my latest A/C venture I have never come across this failure mode before. The system was leaking oil near the compressor and high pressure line. Loss of R134 within a week. I thought the compressor is kaput so I replaced it with a re-manufactured one. I did the following:-

1) System held vacuum down to 30Hg for days.
2) System was pressurized to 60psi for days.

It was holding vacuum and pressure so I charged the system with the correct R134a quantity, 75% of R12 weight. System is ice cold with low side at 45psi and high side at 300psi. All is well except oil is leaking at the crimping joint of the high pressure hose

. It was at 250+psi and the crimping joint is failing. This is the first time a high pressure hose failed on me but it seems to be OK at low pressure. I should have noticed it before changing out the compressor as the hose was oily to touch. I missed the vital sign and thought it was the compressor. Lesson learned for me so beware when you work on yours.

Desert Panther · #6 06-13-2016, 01:55 AM

Quote:

Originally Posted by leathermang

I also think that there is a TOOL for changing out the Schraeder Valve without removing the refrigerant .. that is listed in the archives and possibly in the AC thread in my signature..
NO ONE that I know of suggests putting ' stop leak' into an AC system...
Did you use the correct color of nylog when putting the system together ?

OK, i'd never heard of this tool for changing Schrader valves without losing the refrigerant. So I looked it up on Youtube, and wow! Color me surprised! Learn something new every day I suppose. Thanks for that.

Now if you don't mind, what are your objections to using stop-leak in an A/C system? Is it something you are vehemently opposed to? Or just something that you have had bad experience with? Or you would just rather change the leaking part at any expense rather than using a can of sealer? With some M-B evap cores taking entire days to access (W140), the labor costs and associated parts costs can easily be in the thousands. Versus a can of sealant for a few bucks that "may" solve the problem? Also, there are different grades of A/C stop-leak, just like there are different quality grades of motor oil, tires, etc. I'd expect the top shelf stuff to be effective at some level. Your thoughts and opinions are respected.

leathermang · #7 06-13-2016, 02:20 AM

Quote:

Originally Posted by Desert Panther

OK, i'd never heard of this tool for changing Schrader valves without losing the refrigerant. So I looked it up on Youtube, and wow! Color me surprised! Learn something new every day I suppose. Thanks for that.

Now if you don't mind, what are your objections to using stop-leak in an A/C system? Is it something you are vehemently opposed to? Or just something that you have had bad experience with? Or you would just rather change the leaking part at any expense rather than using a can of sealer? With some M-B evap cores taking entire days to access (W140), the labor costs and associated parts costs can easily be in the thousands. Versus a can of sealant for a few bucks that "may" solve the problem? Also, there are different grades of A/C stop-leak, just like there are different quality grades of motor oil, tires, etc. I'd expect the top shelf stuff to be effective at some level. Your thoughts and opinions are respected.

There are just so many reports of stop leak or anything not originally in tended to be there causing problems.. that hole in the TXvalve is pretty small .. what is to keep it from sealing that up ?
One big problem is that if a leak is on the up side of a curve.. then the likely hood of the sealant getting To it are very slight.. and what is the way in which it ' seals' that hole ?
Just better standard practice to FiX any leaks.. which is why the nitrogen pressure method AND four oz of R22 are used.. they will find a leak in the evaporator ALSO.. and you will never see that leak using one of the leak spotters....
If that stuff does not fix the leak... then you have it in the system if you want to start fresh... do you really want sealer IN the compressor ?
I am going by my reading every where I could find opinions.. hvac and automotive people who do this stuff all the time.. but not trying to sell leak stop...
ACKits.com or Airconditioner. com..
and the MB AC paper manual for the 123 which I have...
AND there is a difference between you using it on your car.. which I have no problem with.. it is a free country.. but I do have a problem with non standard advice going to someone else who may not have done enough reading or have mechanical experience to make a judicial judgement of the recommendations..
Note the AC thread in my signature.. the moderator VStech and I and lots of other people have been building that for years...

vstech · #8 06-13-2016, 01:15 PM

with stop leak, there are a few types. some flow with the oil, and coat the inside of the lines with a barrier that holds back small leaks. there is also a type that will expand into any cracks or leaks and fill the void with glass or a hardening expanding fill upon contact with moisture... the problem is, automotive systems ALL leak. so there is ALWAYS some moisture in the system, so the moisture reacting sealers will harden inside the condenser/evaporator/hoses/reciever/compressor/service gauges... etc.

sure, a 140/124 evap leaker is a pain to fix correctly, but odds are good that a sealer won't fix it either. and you'll be dealing with the sealer when you go to fix it correctly.

as for the vacuum/pressure leak testing... 60 psi is also inadequate for testing.

it needs to hold 250 psi for 1 hour without losing ANY pressure for me to even consider applying a vacuum to it.

vacuum leaks draw in moisture. and a pass from a vacuum leak test is only a 14 psi differential... useless for testing for leaks.

just pressure test, and be sure there is no leak.

simple.

secure.

done.

funola · #9 06-13-2016, 02:09 PM

Why Nitrogen? Here's a table of densities and molecular weights Gases - Densities of some common gases. Molecular weight of Helium is 4, Nitrogen is 28, air is 29.

Wouldn't Helium be best finding leaks?

If you do not have Nitrogen, wouldn't air be just as good since it is very close to Nitrogen in molecular weight? Air is 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide. Air has some moisture in it. Not a big deal if you change the Receiver/dryer to a new unit after pressure testing with air, before evacuating. Thoughts?

Edit: The new receiver/dryer connections will not be pressure tested but will be vacuum tested. A chance you'll have to take if you do not have Nitrogen.

leathermang · #10 06-13-2016, 03:06 PM

Quote:

Originally Posted by funola

Why Nitrogen? Here's a table of densities and molecular weights Gases - Densities of some common gases. Molecular weight of Helium is 4, Nitrogen is 28, air is 29.

Wouldn't Helium be best finding leaks?

If you do not have Nitrogen, wouldn't air be just as good since it is very close to Nitrogen in molecular weight? Air is 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide. Air has some moisture in it. Not a big deal if you change the Receiver/dryer to a new unit after pressure testing with air, before evacuating. Thoughts?

Edit: The new receiver/dryer connections will not be pressure tested but will be vacuum tested. A chance you'll have to take if you do not have Nitrogen.

Nitrogen is available as a DRY gas.. so using it to pressure test also means as it is taken out some moisture is removed.. in home HVAC servicing it is common practice to put nitrogen in three times and take it out ...as a moisture removing procedure..
I think Nitrogen is cheaper than helium ... but argon will also work.. helium left over could be used for balloons BUT be careful.. the helium packaged for that is different from that for welding.. and you do not want to INHALE the wrong one being funny.... as one does not have the gases which tell your body to take in the next breath...
If you use nylog of the proper color and tighten the joints using two wrenches.. you should not have a testing difference between helium and nitrogen...

funola · #11 06-13-2016, 05:08 PM

This is a youtube vid. https://www.youtube.com/watch?v=SsE6TPyTCn0 pressure testing a stationary AC unit with hi side operating pressure of 450 psi. He is testing it to only 150 psi and he gives his reasons. Listen to 0:50 - 1:30, @:30-3:20, 8:30-9:40 if you do not want to listen to the whole thing.

funola · #12 06-15-2016, 11:21 PM

Found a good explanation on why use Nitrogen and R22 together to find leaks from this site What are the Benifits of Leak Testing with Nitrogen?

"Understanding the Basics

System Residues hide leaks. Sludge and residues coat the interior of system components and temporarily seal corrosion pits, fissures, seams, seals, o�rings, and other small leak points. Some of those residues include refrigeration oils, acids, desiccant, pulverized metal, Teflon piston ring material, brazing fluxes, dye particles, etc.
Overcoming Residue Surface Tension: Leaks are harder to find because leak testing is performed with the system turned off. Lost are the benefits of an operating system: a) constant washing of interior surfaces of components; b) higher operating pressures that encourage leaks. With a system at rest, the undisturbed residues mentioned above are able to coat the insides of the evaporator, condenser, compressor, and other components. When Residue Surface Tension is greater than the interior pressures� ability to displace it, there is no leak occurrence, thus no leak detection.

Residue Displacement: If surface tension is the culprit, then how do we overcome it? Answer: By adding 4-ounces of chlorine-based refrigerant R-22 to the system. R-22 disturbs the surface tension. We follow that by pressurizing the system with 175-200 psi of nitrogen. Both are cheap.

At the higher system pressure, the R-22 overcomes the residue surface tension and forces the leak path to reopen. Now, enough R-22 gas is available so that leaks are detected easily. The R-22 is the residue-displacing agent."

leathermang · #13 06-15-2016, 11:53 PM

I suspect they were making that up with expost facto thinking...
I think nitrogen under that much pressure will go through the holes which the refrigerant was going through... without the R-22 added...

The R-22 is added because that is allowed to be legally vented by the EPA and can be detected by a Sniffer... where the nitrogen by itself can not.

BillGrissom · #14 06-16-2016, 12:25 AM

Am I correct to assume that in post 1 you are actually trying to quantify the true vacuum pressure by reading the tiny increments on those gages? Engineers like me are always amazed how the public thinks sensor readings are exact, especially when presented digitally. There is always a +/- error band. In your car, I am pretty sure the 2 gages would see the same pressure when the compressor is not turning and you give time for pressures to equilibrate. The compressor does not make a tight seal from suction to discharge, and the expansion valve is also a metal-metal closure that leaks thru a bit.

Post #4 mentions 300 psig on the high-side causing slight weeping from a hose crimp. That might be a useful "relief valve". I would never want to see 300 psig since you are approaching the point where the compressor stalls as the clutch starts slipping and melts. I had that happen in both my 300D and 2002 T&C van, but we do enjoy >110 F days here that push AC systems over the edge.

Mike D · #15 06-16-2016, 08:50 AM

Quick question for ya Leatherman, you advocate using nitrogen for leak detection. Would Stargon be an acceptable substitute?

I have a tank of Stargon which I use for my wire feed welder. It would be nice if I didn't need to get ANOTHER thing sitting around which I would only use once in a blue moon.

"Stargon shielding gas was developed in the early 80s. The mixture was a three-part mix containing eight-percent CO2, two-percent oxygen and a balance of argon. The goal was to combine the benefits of CO2 and argon/oxygen in one mixture. It worked well and is still used today, but it didn’t completely replace C-25 or argon/oxygen."

http://www.fsmdirect.com/welding/consumables/175-new-shielding-gas-mixture

The O content would be the one thing I question. Introduction of the Stargon would be AFTER a thorough evacuation and vacuum of course.