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Where to look for the leak

cees on Wed July 25, 2012 6:06 AM User is offline

Year: 2008
Make: Fiat
Model: Ducato
Engine Size: 2800
Refrigerant Type: r134a
Ambient Temp: 29 C
Pressure Low: 5 bar
Pressure High: 5 bar
Country of Origin: Croatia

I've been wrestling for almost 2 years now to get the A/C going again.
Added oil, dye and some magic goo from the US that is supposed to seal leaks. The unit works when sufficient refrigerant is added, but stops a few days later. No signs of dye under UV light. Because the condenser is the main exposed part I removed the whole plastic front of the van, a hellish job. But everything looks fine.

My intention was to pressurize the system with argon instead of wasting more expensive bottles of r134a, but I there is still 5 bar (70 psi) with the compressor not running. It has been standing for approx 2 months now with no change in pressure, so this must be a very peculiar leak, because even a pinhole in any metal part would have emptied the system. The only part I did not yet investigate is the evaporator because the whole interior trim must be removed, but I poured water in the air ducts that should transport traces of dye if the leak is in the interior unit.

What is the usual suspect for a leak that is only there when the system is operating?

mk378 on Wed July 25, 2012 8:31 AM User is offline

At this point it doesn't matter. Having added the "magical goo" you are now committed to replace everything anyway. Were you to open the system, the goo will harden throughout and ruin all your parts.

Static pressure stays about the same as a charge leaks out. The pressure is just the vapor pressure of the liquid. As long as there is one drop of liquid somewhere, it stays the same.

cees on Wed July 25, 2012 1:50 PM User is offline

That sounds bad, real bad!
I payed a lot of money to get this can of snake oil across the Atlantic and now you tell me I've got to replace everything. And the stuff doesn't even do what it is supposed to, because it didn't stop the leak at all. If it were any good, I could have left it in the system, at least that's what the label on the can said.
Isn't it possible to flush the system with a solvent, disconnect a hose at the lowest point and let it drip out?

cees on Sat July 28, 2012 9:21 AM User is offline

You've really scared me.
After several hours searching the web, I'm still in doubt. There are a lot of comments like yours, but also guys who claim they filled more than 200 AC systems and never encountered as much as a blocked orifice.
I do not intend to find out what happens if I open the system, so I am sort of doomed to keep it charged.

The good thing is, I finally found yellow traces of dye around the bottom of the high side pressure switch, so that surely is a leak. If the sealant is any good at all, it should be able to solve the problem there. If the situation doesn't improve, I will have to unscrew it and install a new seal or O-ring or whatever the manufacturer used there.

jglanham on Sat July 28, 2012 1:18 PM User is offline

There are two types of sealer products. One has a chemical additive that swells shaft seals and "O" rings and is not dangerous to your system. The other type contains a chemical that hardens when exposed to air, similar to a radiator leak stopper. That is the one that will cause disaster to your system. Do some research on the product that you put in your vehicle. Your comment about it not leaking for two months, but leaks when running (higher pressure in system) sounds like you might have used the less harmful product. Hopefully, the "O" ring on the pressure switch is the only problem.


AutoCool on Thu August 09, 2012 6:59 AM User is offline

cees, I've recently seen 3 motorhomes based on the Fiat Ducato that had leaks from the hose connections on the rear of the compressor. These have all been the Sanden SD7V16 compressor model 1178 with the rear plate stamped "VUD". It seems the oring grooves in the plate are too shallow. When you bolt the AC pipes on the compressor, the orings don't get compressed at all. That diesel motor shakes a lot and the shaking seems to create leaks while you're driving.

What I've done is file down the mounting pad just a bit, half a millimeter or so. Then the orings should seal the connection just fine.

Also, these compressors have a machined hole in the actual mounting bolt hole near the letters "VUD R" on the rear plate. The compressor was actually leaking from that hole. I guess it was a poor machining or maybe a small crack. Very very small leak but maybe yours is leaking the same only worse. 1178 leak.jpg

AutoCool on Thu August 09, 2012 7:04 AM User is offline

Sorry, here is a photo I took of the leak.

Leggie on Thu August 09, 2012 11:12 AM User is offline

Pull the R134a. Put enough R134a back in to bring it to 1atm. Pressurize to about 15atms (150 psi or so) with N2 or Ar. It doesn't matter.

Hook up a gauge to one port. Check that port for leak with sniffer. If it tests fine, move the gauge to other port. Then Check the first port for leak. After that, spray every connection with soapy water and look for bubbles. if you don't find any leaks, the leak is at hidden connections, evap or condenser or the compressor shaft.

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