A/C Chargeing question.

[acardon]

Is any vacuum loss acceptable? I pulled a vacuum on my A/C system a few days ago. Got it down to 28" and let it run for about an hour. Shut the valves and let it sit. It's lost about 1 1/2 inches of vacuum.

[Larry V]

It is better to use dry nitrigen for leak test. I use around 100psi. Let it set for a hour or two. Temp will not cause any pressure changes.

[rayharris]

If you lost vacuum, you have a leak somewhere. As above add 100 psi nitrogen to it and use soap bubbles in obvious places and try to find and repair leaks.:anim_25:

[acardon]

If you lost vacuum, you have a leak somewhere. As above add 100 psi nitrogen to it and use soap bubbles in obvious places and try to find and repair leaks.:anim_25:

I was affraid of that. I don't have any nitrogen. A friend has a lead detector. How much pressure will a can of 134 put on the system? Will that be enough to leak test? Thanks.

[rayharris]

About 40 lbs depending on the ambient temperature. welding supply houses will have what you need. the 134a pressures are better than nothing at all. You have a small leak somewhere. Look for oily spots.:anim_25:

[Gregs210]

1.5" in an hour. You will never be able to find that small of a leak with soap. An electronic leak detector might find it. The drop could be a system leak, a manifold gauge hose connection, or a gauge valve leaking.

I don't think I would worry much about it. I think I would charge it and go on.

[acardon]

About 40 lbs depending on the ambient temperature. welding supply houses will have what you need. the 134a pressures are better than nothing at all. You have a small leak somewhere. Look for oily spots.:anim_25:

It's a new system. Compressor hasn't been run. I doubt that the oil has left the compressor. I'll borrow the leak detector. I hope it's not one of the swedge fittings, I paid way too much for. :rolleyes:
http://pic100.picturetrail.com/VOL678/4398712/9300251/393767030.jpg

[Rick_L]

You have a leak, and you may as well find it now. Check all your fittings for tightness, if no problems there, then take each apart and look for torn/nicked/missing o-rings. Check your schrader valves and any switches that screw into them. That will take care of the easy stuff. If you don't find anything, then you can charge with one can and leak detect.

Actually you have a pretty big leak if you only got to 28" vacuum initially, and lost 1-1/2" from there.

[crankshaft]

You, sir, are in very good shape. That small loss could very easily be in your gauges. Charge her up and enjoy it.
You will not have a problem with that. :anim_25:

[acardon]

Lots of openions, but I think I'll look for a leak. I thought about the charging connections and removed the high side to eleminate it. It could be the switch that screws in the dryer. Thanks guys.

[roger1]

I would try it again.
You could have still had some moisture in the system that would have boiled down and lose some of vacuum.

[Rick_L]

That would only occur if the original vacuuming was either not done long enough or the temperature was too cool. Too cool is probably not a problem in TX in late April. If the temp is above 75-80º and you vacuum for an hour, that's sufficient if there's no leaks. You have to achieve a vacuum that's representative for your elevation. In the DFW area that's in the 29.50" Hg range.

[roger1]

Since his vacuum pump can only pull 28.5 inches, it will take longer to boil the moisture. It wouldn't hurt anything to run the test again to see if he gets the same result.

[coolhand55]

Evacuating a system properly depends on a lot of factors. Ambient temp. is the least of your worries. The time required depends on quality of pump, guages, hoses, restrictions(schreaders etc.) amount of moisture/non-condensibles to be removed and so on. A "good" vacuum should be measured with a Micron guage. If I remember correctly, 29.92"Hg. = 760,000 microns. An acceptable vacuum is 500-1000 microns held for 20-30 Min. Due to components used in auto A/C systems this is difficult to atain. For leak testing pressurize the system with dry nitrogen to 100 PSI. and check again in 24 Hrs. or so. If press. drops there is a leak. Find it with soap and repair.
This is just a basic description. Hope it helps. Good Luck:tu:tu

[Bihili]

I would apply vacuum again and leave the gauge on over night.
This should give you a more accurate reading of your situation the next morning.