I just put a system back together with new hoses, o-rings, etc. and it holds vacuum well (29+ for half our). Still, before I commit the precious R-12, I'd like to test under positive pressure. Not having compressed nitrogen handy, is it really bad to test with dry air? By dry I mean I've got a moisture bowl and air filter on the compressor. I'm using the old drier until I'm ready to charge so I'm not concerned about ruining it. I just want to pump it up to 100 psi and then use soap & water to check joints. If it all checks out then I'll replace the drier, evacuate and charge!
It all depends on how much moisture is introduced into the system. Air is not the issue so if it is clean a good evacuation will remove the trace moisture. If you introduce to much moisture you have a chance of causing issues.
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If it holds the vacuum for an hour, I'd charge it up.. A half hour is good, but an hour, I'd go for it..hope this helps..
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Chick
Email: Chick
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Freedoms just another word for nothing left to lose
Air is not a good test medium for AC leaks. Have seen many instances when this process was used and the results were negative, yet the system did leak refrigerant.
Why the vac looks good, but in some instances the vac hold will be good and the system will leak under pressure. After charging, perform a very through leak test evaluation of the system.
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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson
I wouldn't rely on the vacuum test either.
The only way to test reliably is the same way the system will operate I.E. under pressure.
If you have a split or crack along the length of a hose, a deep vacuum will cause the sides of the split to close up. Pressure would force it open.
The same would happen with a loose connection - vacuum would pull it tighter together, pressure will force it apart.
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Vic @ Pennine AutoChill
You can use r134a for pressure testing which is much cheaper than R12. Just be sure to remove it all before charging with R12.
Can you really remove it all without disassembly? If a little R-134 mixes with R-12 is this really bad? Will the R-134 contaminate the new ester oil I have in the system now?
BTW, I did pressure test with air at around 100 psi. I saw no bubbles when joints were sprayed with soap & water solution. I realize this is probably not going to detect any small leaks....
By getting all the 134a removed you just recover it or whatever your method is for removal and you will be fine. You are going to pump the system down anyway, right, before you charge with R12? I'm not sure about using ester oil with R12 though. Mineral oil is generally used for R12. Perhaps someone else can set you straight on this.
Edited: Sat November 07, 2009 at 7:24 AM by hjc149
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