AC vac results with question - PeachParts Mercedes-Benz Forum

JimmyL · #1 04-24-2006, 06:51 PM

I found a leaking high pressure schrader valve on my '85 wagon's AC system. Not sure if it is my only leak, as freon was desperately low. I resealed the connector with nylog on the threads and replaced the inner valve.
This was the only leak the sniffer detected at that time.
So, I then pulled a vac on the system for an hour, then closed the valves to check on it holding a vac. It moved from just short of 30 psi (whatever unit) to almost 29 1/4 in one hour and 20 minutes. (loss of maybe 1/2 to not quite 3/4)

Is this a substantial leak, or an inconvienent leak? (once a week vs once a season for example?)
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R Leo · #2 04-24-2006, 06:58 PM

I'd be suspicious. Leave it overnight and see if it changes any more. If not, you should be good to go. If you loose any additional vacuum, pressurize w/refrigerant and recheck for leaks...particularly that highside valve you nylogged.

JimmyL · #3 04-24-2006, 07:16 PM

Quote:

Originally Posted by R Leo

...particularly that highside valve you nylogged.

Should I have tried to seal those threads with something else?

dmorrison · #4 04-24-2006, 07:41 PM

You sealed the threads correctly. The Nylog is extra help, not required. The guages should hold rock solid after shutting off the vacuum pump AND closing the valves on your guages. This way you are reading just from the system.

You may have to put a small charge of Freon in and sniff for it. Correct any leaks and try again.
Once the system is solid. Pull vacuum for 3-4 hours. The vacuum pump will get hot. Let it sit overnight to sublimate the moisture in the system into a gas and then vacuum it again for an hour or so. Add your freon, 2.2 Lbs of R-12 or 80-85% of that for R134. ( it will be a better system with R12. I did the R134 conversion with a parallel flow condensor and went back to R12 when the Compressor failed.)

If R134 then charging to vent temps is a good method.

If your compressor failed you should replace the manifold rubber hose section, by either replacing the hose or having it rebuilt. Kims Hydraulic in Ft. Worth has done mine.

Dave

JimmyL · #5 04-24-2006, 10:51 PM

Well darn! It's down to 26, so a leak remains....

What I may do since I have 2 oring kits, is replace and Nylog the seals at the exp valve, rec/dryer, and any other joint that presents itself. Maybe I will luck into the leak, and if not, well no real harm done. Have to charge it anyway, so might as well try something. If I don't, I know it's gonna leak.
I had zero leak around the compressor according to a really nice borrowed heated diode-type sniffer. (very cool tool!) That was my original worry, but not so much as a peep when it still had some freon.
Well, more to follow I guess. thanks for the help so far.....

dmorrison · #6 04-25-2006, 02:34 AM

Jiimmy are you doing R12 or R134?

Evacuate the system again and open a freon can into the system. This will charge the system enough to detect a leak. "Of course you will recover the freon after finding the leak".
Use the sniffer and go over every part of the system. Compressor fittings and front seal. Manifold hose, all connections. Condensor including ALL the serpentine tube. The hose to the dryer, all its connections (Pressure switch and 2 hose connections, the temps switch is not a problem) The high pressure hose into the cabin. The hose connections at the expansion valve and then follow the suction hose back to the compressor. Stick the sniffer in the center vent, real far into the vent. If it chirps a little more then remove the black rubbery material around the expansion valve to evaporator connection tubes. Stick the sniffer into the evaporator box. If the evaporator is leaking the sniffer will fire off at this point. My daughters car would chirp just a little more in the vents and around the expansion valve. But when I put it into the evap box it fired off. YOU DO NOT WANT THIS TO HAPPEN. It means the evaporator is leaking. If you have to replace the evaporator I have lots of pictures of everystep in both the 300TD and the 240D. Let me know if you need them.

Dave

JimmyL · #7 04-25-2006, 09:42 PM

I'm starting to think this AC work thing is getting the best of me. (which ain't that great, btw....)
Decided to replace 4 o-rings at exp. valve and the o-rings to rec/dryer prior to my next round of leak detection. The old "try something first at least" approach. Then if I hit the leak by chance, great!!
Well, the other side of that coin would be making the leak worse. MUCH!!

Pulled a vacuum for 2 hours, then closed the guage valves, turned off pump, and took youngest daughter to piano then to her softball game. Got back and after 4 hours it had dropped from 29.5 to 20!!!!

F

I remember someone who had so much trouble installing exp. valve that they went inside for awhile, just to walk away. Mine went alarmingly easy, both in and out. Nylog'd everything too. Now it's worse.
Sigh.....
Well, now I will put in a can and sniff for at least a couple of leaks probably.
No wonder Autozone loans these tools out for 90 days......

imdavid28 · #8 04-25-2006, 09:58 PM

Quote:

Originally Posted by JimmyL

Well, now I will put in a can and sniff for at least a couple of leaks probably.
No wonder Autozone loans these tools out for 90 days......

You can rent R-12 vacuum pumps and gauges from Autozone?

dmorrison · #9 04-25-2006, 09:58 PM

Your following a logical order. But if the leak is in a metal part, evaporator or condesor then the Orings replacement will do nothing. Its now time for some freon and the sniffer.

Another consideration. If the leak is in the metal tubes etc. then messing with the connections can make the crack/hole bigger.

Dave

vstech · #10 04-25-2006, 10:49 PM

another way is slightly pressurize with dry nitrogen. checking for a leak with a vacumme on the system is BAD. it introduces water vapor to the system. best way is with pressure. I mean really, what will show a leak faster 100psi or -15 psi? atmo is 14.7psi, and best vaccume is going to show 29.6 or so inches of mercury, and any leak that is present will put moisture into the system. I use 22 or dry nitrogen to test for leakdown, best way IMHO
John

JimmyL · #11 04-26-2006, 12:33 AM

First, we want things not to break. If they do, can they be easy to fix.

NO

Well, charged the wagon with a can of freon. Slurped up the whole thing, although a pan of warm water was needed for the final bit.

Let it run a few minutes, then turned on AC for awhile. Turned off car and got the sniffer. NOTHING! Anywhere! Sniffer is perfectly happy with a freon-free environment. Tried it briefly near the spent can of freon and it went nuts. (great tool!) So, can't find my quickened leak.
Gets better.
Bought an AC DVD from Autozone the other day. Good informative basic AC video. I recommend it to those like myself, with no AC background.
Anyway, hooked up the guages, and both the high and low sides had equalized around 70 (remember, its low with only one can)
OK, start the car with gauges attached and turn on the AC.

Well, the low pressure side went to minus 6 (as in below 0 in the vacuum portion of guage). High side was 95. AND, the upper right line @ expansion valve froze up (whole exp valve very cold and condensating). This is one of the lines to/from evaporator.

So, besides a leak that I can't sniff, has my expansion valve decided to roll over on it's back, lift it's skirt, and pick this point in time to die???

Thanks in advance.

I talked myself off of the ledge by reminding myself that at least the wagon wasn't smoking.....

I did have proper ventilation....

Pete Burton · #12 04-26-2006, 08:50 AM

Great pictures, Jimmy. I think that expansion valve is suspect. Since you have gone through the valve connections already, I'd replace it. Surprisingly, that valve is only about $20.

R Leo · #13 04-26-2006, 09:45 AM

Quote:

Originally Posted by JimmyL

the low pressure side went to minus 6 (as in below 0 in the vacuum portion of guage). High side was 95.

There's nothing wrong with that TXV, your system is still undercharged. IIRC, hi side should be in the 300psi region, low side in the realm of 30-40psi.

imdavid28 · #14 04-26-2006, 10:52 AM

Quote:

Originally Posted by JimmyL

I talked myself off of the ledge by reminding myself that at least the wagon wasn't smoking.....

I did have proper ventilation....

I LOVE THE VENTILATION SYSTEM!

SD Blue · #15 04-26-2006, 11:33 AM

Quote:

Originally Posted by JimmyL

I did have proper ventilation....

Yes, definitely the hallmarks of a Texas garage!

I have a couple of high-volume fans which can feel like a windstorm if you are not used to it. My next project will be adding a mister system to go with all of that air.