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Can't pull more than 10" of vacuum. Won't hold for more than 3 seconds.

lambertjohn on Tue September 06, 2011 4:38 PM User is offline

Year: 1996
Make: Volkswagen
Model: Golf
Engine Size: 2.8
Refrigerant Type: 134
Ambient Temp: 83
Country of Origin: United States

Something tells me I'm destined to not have cold AC in my old VW, but I'll ask anyway, then I'll quietly slide away to lick my wounds...

I just got through with a major AC rebuild on my 96 Golf. New compressor, new expansion valve, new drier, new condenser, old hoses (thoroughly flushed), and old evaporator (also thoroughly flushed.) I also replaced all the o-rings with new ones. I really took my time on this job and tried to do everything right. But....Today, I got out my Mastercool vacuum pump and HF gauge set to draw a vacuum and charge the system up. I hooked everything up. Blue to low side, red to high, yellow to carry the vacuum down to the pump.

When I was happy everything was in place, I opened up the valves on the hoses/gauges and switched on the vacuum pump. It whirred to life, and as the low side gauge started to move, a smile crept across my face. But my smile quickly faded not ten seconds later.

Seems the most vacuum I can pull is 10hg. That's right, 10". When I shut everything down to see if the 10" will hold, the low side gauge immediately drops to zero. It doesn't hold for even one second which tells me that I've got a major breach in the system somewhere.

I'm thinking to myself, do I really have that big of a leak in the system where I can't even hold a vacuum for two seconds? Maybe I've just got a defective ball valve on the low or high side ports? Can they be replaced? Or maybe the quick connects on the HF gauges are defective? But when I disconnect the high and low side hoses from the ports on the car, the gauge jumps to 29hg, so I think the gauge is working fine as well as the vacuum pump. Maybe one of my new o-rings is just not the right size, or I bent/crimped it when I put the fitting in causing a huge gap in the system (would a mis-sized o-ring cause such a drastic loss of pressure so quickly?)

I'm a newbie, so I could sure use some professional opinions out there. Surely someone out there has run into this kind of situation before?

Maybe I just have a big old hole in the system somewhere? If so, where would you look for such a hole? The evaporator? I guess it would have to be pretty extreme for the system to lose vacuum in under three seconds.

Thankfully, it's starting to cool down here in Dallas, so maybe the Big Man in the sky is throwing some cool air my way until I can figure this thing out. Any help you guys can give me would also be appreciated.

Thanks all!!

Edited: Tue September 06, 2011 at 5:34 PM by lambertjohn

540itouring on Tue September 06, 2011 5:58 PM User is offline

First off all O rings should have been coated with compressor oil to ensure they seal and seat ok. The filter drier will also require replacing as after 4 hours exposed to air they are no good but find the leak with this one fitted first or you will do another one in . I would say you have a big leak and should hear a hiss sound from leak area . I would check the pipes / seals to the compressor first. if you have no luck the best way is to pressure the system with OFN and you will soon find the leak but another way i have done to save expense is to disconect parts from the system , blank hoses off with oil coated rubber bungs and see if you call pull a vacc. Once you can pull a vac you then know what part of the system has the leak. Then you can check that part and repair as required. I hope that helps to start with .

lambertjohn on Tue September 06, 2011 6:11 PM User is offline

Thanks 540. That's what I was thinking of doing, disconnecting parts of the system and seeing if I can pull a vacuum on the remaining parts. I'm going to start with the evaporator, since it's the only component I couldn't lay my eyes on as it's tucked way up inside the dashboard. What I'm going to do is disconnect it from the high and low ports, then plug the ports and try and pull a vacuum on the rest of the system. If I can indeed draw a vacuum, then I'll know the leak is in the evaporator. At least that's how I hope it will work.

By the way, I did coat all my new o-rings with PAG oil and I meticulously matched the new ones up with the old ones, to make sure I got the right size. They all seemed to fit snug and well. But maybe I screwed one up somewhere? I'll report back with my findings. Thanks again!

lambertjohn on Wed September 07, 2011 12:22 PM User is offline

Thanks 540. Did what you said and found the leak. Evidently, my evaporator is shot. I'm guessing there's a sizable hole rusted in it somewhere but I won't know until I get it out of the car. Which of course, is a task of monumental proportions. So now I have to regroup, take a deep breath, and find a day or two to disassemble my entire dashboard and go at it. I'm probably going to go ahead and replace the heater core while I'm in there as well. Wish me luck. Thanks again!!

HECAT on Wed September 07, 2011 1:17 PM User is offline


HECAT: You support the Forum when you consider for your a/c parts.


Edited: Wed September 07, 2011 at 1:19 PM by HECAT

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