Will an AC System maintain a vacuum?

[wildbill23c]

I evacuated the AC on my 88 Bronco 2 a couple weeks ago and the gauges showed a good vacuum and maintained at -28 for at least the hour I left the gauges hooked up. 2 weeks later (today) I hooked up the gauges and they're showing -13. Is this normal for the vacuum to slowly dissipate over time?

 

[4x4junkie]

I wouldn't think so, but I can't say for sure since the seals are mainly designed to retain pressure, not vacuum.

When I did mine, I left it overnight and the vacuum stayed put, but I didn't let it go any longer than that (I wanted my A/C working again )

 

[wildbill23c]

Realized after I hooked up the gauges again, the yellow line on my gauge set was lose so it was returning to 0 LOL. Not to worry I'm in the middle of putting everything back together right now, got the compressor oil drained and filled with new oil, and going through and replacing all the o-rings right now, just put in the new orifice tube, and getting ready to put the new accumulator/dryer assembly in. Have to wait till payday to get refrigerant though .

 

[adsm08]

If the system is properly sealed it will hold a vacuum indefinitely. Your drop to 13 was probably due to unhooking and then reattaching the gauges.

Static pressure on an AC system is usually between 30 and 100 PSI, depending on temp in the engine bay. Atmospheric pressure when under vacuum will be at most 14.7 PSI. If the refrigerant doesn't get out air won't get in.

 

[wildbill23c]

Thanks adsm08. I think my gauge set was leaking a little bit, tightened some connections and seems to be holding steady well until I disconnected the gauge set again and reconnected it LOL, then it dropped a bit. I've gone as far as I can until I get refrigerant to charge the system. Going to add leak detection dye as well so I can see if I have any leaks anywhere. Can't imagine the first attempt being successful given I disconnected every part of the system LOL.

 

[wildbill23c]

Well looks like the compressor is shot, it worked for about 5 minutes then stopped building pressure, and then the clutch would try to engage and just squeal. Thinking that it was damaged by the PO since when I tried to drain the old oil out I got maybe a teaspoon of old oil out of it. I also find it odd that the oil that came out was an orange color, I thought the refrigeration oil would either be a green color or clear since the new oil I put in is clear.