Automotive Air Conditioning Information Forum (Archives)

seagull369 on Thu August 07, 2014 10:14 PM

I was vacuuming down a system today and, after running the pump for about a half hour, I returned and noticed some bubbles forming behind the site glass on my manifold set. I took the set down off the hood latch and moved it so the oil in the cavity pooled towards the bubble area saw the bubbling increase. I'm thinking I have a leak there but just wanted to confirm with you guys.

The gauges were reading about 25 inches of mercury while this was happening, so ya'lll know..

wptski on Fri August 08, 2014 7:49 AM

One thing is after 30 minutes you only have 25"/hg, what kind of vacuum pump are you using? I see that within minutes, unless I just have a much better pump?

No sight gauge on my manifold but I do find system oil in my hoses at times. If you don't watch how you shut down your vacuum pump, you can pull its oil into the hoses, etc.

seagull369 on Fri August 08, 2014 12:04 PM

seagull369 on Fri August 08, 2014 12:07 PM

I meant to say (~29 or so) inches .

mk378 on Fri August 08, 2014 5:52 PM

The test is to close the valve wheels, so the vacuum pump is no longer connected to the car, and watch if the low side gauge moves up. If it does, there's a leak.

The sight glass in a manifold is a gimmick feature. It has pretty much no practical use. More expensive full-professional manifolds don't have them.

seagull369 on Sat August 09, 2014 6:47 PM

Thanks for the replies. I was wondering, though, if I have a leak in the seal of the site glass. I wouldn't think I should be seeing bubbles in that area, esp after a half hour pull down.

Dougflas on Sat August 09, 2014 7:06 PM

Quote
Originally posted by: mk378
The test is to close the valve wheels, so the vacuum pump is no longer connected to the car, and watch if the low side gauge moves up. If it does, there's a leak.



The sight glass in a manifold is a gimmick feature. It has pretty much no practical use. More expensive full-professional manifolds don't have them.

I have to respectfully disagree. The TEST 550 series are professional manifolds and in fact have sight glasses. One of the features of a sight glass is to be able to monitor the liquid refrigerant entering the manifold. NPR makes a sight glass that connects to the third hose at the manifold. Some refrigerants must be charged as liquid and do need a sight glass.
If you think the seal at the sight glass is leaking, close both handwheels and put the third hose to a refrigerant source. Use bubble search at the sight glass to see if there is a leak.

wptski on Sat August 09, 2014 8:08 PM

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Originally posted by: Dougflas
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I have to respectfully disagree. The TEST 550 series are professional manifolds and in fact have sight glasses. One of the features of a sight glass is to be able to monitor the liquid refrigerant entering the manifold. NPR makes a sight glass that connects to the third hose at the manifold. Some refrigerants must be charged as liquid and do need a sight glass.

If you think the seal at the sight glass is leaking, close both handwheels and put the third hose to a refrigerant source. Use bubble search at the sight glass to see if there is a leak.
Yes, like R410A that must be charged as a liquid but if you have to charge on the low side while running, you don't want to see liquid or you will slug the compressor therefore you have to throttle it in.

Dougflas on Sat August 09, 2014 10:40 PM

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Originally posted by: wptski
Quote
Originally posted by: Dougflas
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I have to respectfully disagree. The TEST 550 series are professional manifolds and in fact have sight glasses. One of the features of a sight glass is to be able to monitor the liquid refrigerant entering the manifold. NPR makes a sight glass that connects to the third hose at the manifold. Some refrigerants must be charged as liquid and do need a sight glass.



If you think the seal at the sight glass is leaking, close both handwheels and put the third hose to a refrigerant source. Use bubble search at the sight glass to see if there is a leak.

Yes, like R410A that must be charged as a liquid but if you have to charge on the low side while running, you don't want to see liquid or you will slug the compressor therefore you have to throttle it in.

you should be using an expander so you don't slug a compressor

wptski on Sat August 09, 2014 11:03 PM

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Originally posted by: Dougflas
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you should be using an expander so you don't slug a compressor
You mean a liquid to vapor adapter which is just a adapter with a pinhole in it? No need for sight glass then. I have one but so far I've charged my full charge using liquid on the high side with system off after evacuation.