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Won't hold vacuum/how to find leak on R12

cam76034 on Thu September 18, 2008 1:12 PM User is offline

Year: 1991
Make: mazda
Model: miata
Engine Size: 1.6L
Refrigerant Type: r12
Country of Origin: United States

Suspected the TXV needed replacing. After replacement I can't get it to hold vac, even though it would hold before I replaced it. I've gone back and put in new metric size 0 rings on the ones I replaced before, but it still loses vac. What's the best way to troubleshoot where the leak is on an r12 system without using up the few cans I've got ? I do have some R22, could I use that to sniff it out?

Edited: Thu September 18, 2008 at 1:37 PM by cam76034

Cussboy on Thu September 18, 2008 2:45 PM User is offline

Yes, you could use the R22 for leak detection, or even R134a if you had the right fittings. Obviously, you know your leak is likely to be where you just re-did fittings, like your TXV or the evaporator. Are your new O-rings thick enough? did you use a little oil or Nylog on those?

Edited: Thu September 18, 2008 at 2:46 PM by Cussboy

cam76034 on Thu September 18, 2008 3:53 PM User is offline

I have 134 fittings, just not sure how I'm supposed to leak test an r12 system using 134. What about the oil ? Didn't have any nylog for o-rings btw.

mk378 on Thu September 18, 2008 4:23 PM User is offline

Temporarily put a conversion fitting on the car and use your R-134a gauge set. Charge to about 50 psi. You don't want to charge so much that there is liquid R-134a in the car, because then the pressure won't drop as it leaks out.

R-22 is fine too, has the same fitting as R-12 on the tank. But it's more expensive and more potentially environmentally damaging than R-134a, though the EPA does seem to approve of the use of small amounts of R-22 for leak tests.

You don't need to worry about having compatible oil because you won't be running the compressor.

cam76034 on Thu September 18, 2008 5:12 PM User is offline

Thanks mk378! So I can just add, say 1 can of 134? Will that bring it up to the 50psi you mentioned, or am I supposed to do something else in addition? Then use some dye and UV, I guess? I thought I'd have to run the compressor in order for it to go through the system in order to find the leak, apparently that's not the case.

TRB on Thu September 18, 2008 6:21 PM User is offlineView users profile

If you plan on using another refrigerant beside the R134a. Do not run the system, just let the pressure of the can and or vacuum pull in the refrigerant.


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mk378 on Thu September 18, 2008 6:33 PM User is offline

This is a "static" test, engine off the whole time. Dye does not move to the leak locations without the system running so it is not used for this test.

Put the system under pressure and find where it leaks out. Ideally this is done with an electronic leak detector. That's why a refrigerant is used instead of inert gas, it can be detected. If you don't have an electronic detector you can try soapy water on all the connections. In that case you wouldn't have to use refrigerant, air or nitrogen could be used instead. With air you don't want raw air from a compressor because there is often slugs of water in the hose too. Inert gas can be filled to a higer pressure because it doesn't condense like refrigerant would. Do not go over 150 psi though because that's about all that the evaporator and compressor shell can stand.

If you don't find any leaks you want to see if the pressure goes down. Leave the gauges on and walk away for a few hours. If the pressure stays up right where it was you can assume there is no major leak and go ahead and evacuate and charge with R-12.

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