Are manifold gauges vacuum-rated?
- Thread starter tarantino
- Start date
Typical manifold gauge hoses can slowly leak, especially when they get older. But I've found after years of service work if the systems shows a slow leak with a gauge set hooked up there is a leak somewhere. Best way to test for a leak is to pressurize the system. A system could appear leak free with a vacuum test but have a leak when pressurized. (A vacuum test is only 29.9 inches of vacuum, a pressure test is 150 psi). FWIW
Yes, thanks. As of now, I know the manifold leaks. I redid the evacuation and closed off the LP valve. The pressure in the manifold dropped exactly the same way after a few hours.
RPH
Well-known member
Over several hours temperature change and any left over substances will boil off or change the reading,
fitter30
Well-known member
Pressure test with nitrogen with 500 lbs. Nitrogen won't change pressure with temperature fluctuation.
Can you explain this? Nitrogen follows the ideal gas law. And anyway, air is 80% nitrogen.
When you evacuate a system, you're dropping the internal pressure low enough that any liquid (such as moisture and freon) will evaporate and be able to be drawn out as a vapor. Nitrogen evaporates at -320 F, so - for all intents and purposes - it's a gas at standard temps and pressures and doesn't change much at all.
For pressure testing, nitrogen is an ideal choice, because it's inert, non-corrosive, and non-flammable. Freon/oil mixtures and oxygen (or air) can explode under pressure. Plus commercial nitrogen is dried so as not to admit moisture into the system.
A digital micron vacuum gauge is very helpful when trying to detect if a system leaks. The resolution of an analog manifold gauge set is not fine enough to see a leak. I do automotive A/C and when my low side analog gauge shows 29.9 inches of vacuum, the system still has a long way to go. Basically, my micron gauge STARTS reading when my analog gauge APPEARS to have reached 29.9 inches. Hell, the needle of the analog gauge is too wide to be accurate enough when it comes to vacuum levels deep enough to actually remove moisture, or see a leak. My micron gauge STARTS reading at 9000 microns (remember, at this point, my analog gauge already APPEARS to be a 29.9) if the system has a leak, there is no way I can get down below 3000-4000 microns. (which is not visible on the analog gauge) If my micron gauge stops going down around 3-4 thousand, and it appears all vacuum progress has stopped at that point, I shut the pump off and start looking for the leak. The last vehicle I charged, I vacuumed down to 1000 microns. Some guys say you should get down to 500 microns but that is hard to do with an automotive system. A 500 micron vacuum level is much easier to achieve on a hermetic system..... and if you do get that low, then you can pretty much guarantee there is no leak.
Also, if you suspect your service port connections are leaking and making it impossible to achieve a deep vacuum, get yourself some Nylog Blue refrigerant thread sealant. Do a youtube search for Nylog and see how to use it. It's made from refrigerant oil, but it's thicker and it helps to seal A/C connections.
Also, if you suspect your service port connections are leaking and making it impossible to achieve a deep vacuum, get yourself some Nylog Blue refrigerant thread sealant. Do a youtube search for Nylog and see how to use it. It's made from refrigerant oil, but it's thicker and it helps to seal A/C connections.
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Yes, I know you can't rely on the manifold to read the vacuum accurately.I know Nylog well, though I wasn't using it now. I will do the final evacuation without the manifold.
Yeah, I considered getting a digital micron gauge - then was told I had to have a separate one for each of the refrigerants I was working with. I didn't know if I was getting a sales pitch just to buy more stuff, but when I worked at Sears I might be required to work with R-12, R-22, R-500, R-502, then R-410a. Would have gotten prohibitive, so I just bought several manifolds and kept them separate. Luckily I ended up only doing high temp so didn't need to get multiple vacuum pumps! 
I do have to wonder what difference it makes what refrigerant one will use when vacuuming an empty system.Yeah, I considered getting a digital micron gauge - then was told I had to have a separate one for each of the refrigerants I was working with. I didn't know if I was getting a sales pitch just to buy more stuff, but when I worked at Sears I might be required to work with R-12, R-22, R-500, R-502, then R-410a. Would have gotten prohibitive, so I just bought several manifolds and kept them separate. Luckily I ended up only doing high temp so didn't need to get multiple vacuum pumps!
It's the refrigerant oil. Some always gets removed with the gas, and - along with moisture, sludge, and other contaminants - it mixes with the oil in the vacuum pump. And since vacuum pump oil is specifically made for low vacuum operation, any contamination affects it's solvency. (It's why pump manufacturers state you should change your vacuum pump oil after EVERY evacuation. But that would be cost prohibitive).
The oil problem became much worse with the advent of R-410a and R-134a. Their oils are not mineral like most of the old gases. System contamination - and thus cross contamination between manifolds and pumps - made it mandatory to have separate gauges and pumps if you worked on the different classes of refrigerants. It's why many techs no longer will work on any R-22 systems. It's not worth the expense and complexity of carrying separate stuff on the trucks for an "obsolete" class of refrigerants.
Notice, too, when you get your car worked on that the mechanic has separate recovery stations so as to prevent cross-contamination. It ain't cheap!
Ok but why a different micron gauge for each refrigerant?
The different oils require specific elastomers (i.e. rubber O-rings and seals) and the newer oils will degrade and dissolve some of the older seals. Over time, they will leak - which you obviously don't want if you're testing a system for leaks.
pcmeiners
Well-known member
"Plus commercial nitrogen is dried so as not to admit moisture into the system."
Commercial nitrogen is not dried for that reason, drying results from the processes used to separation nitrogen from air by various methods.
One of the main points of multiple purges is the dry nitrogen carries moisture out of the system due to the vapor pressure of water. Without evacuation and introduced nitrogen following it, water vapor is much more difficult to remove and timely.
"Some always gets removed with the gas, and - along with moisture, sludge, and other contaminants "
If you are evacuating gas at a reasonable rate extremely little contaminates/sludge are carried along with the gas vapor., For it to carry contaminates the gas would have to to be causing a mist (fast boiling) within the system. Water vapor is readily carried with the evacuated vapor.
As to a micron gauge for $100, you might get lucky with a "mainland special". On the other hand I order (2) new Elitech gauges, both arrive DOA, first one had a slow leak, the second had a fast leak, Finally I purchased a Yellow Jacket, with a detachable vacuum sensor, which was leak free. Even the expensive gauges have a tendency to leak.
Commercial nitrogen is not dried for that reason, drying results from the processes used to separation nitrogen from air by various methods.
One of the main points of multiple purges is the dry nitrogen carries moisture out of the system due to the vapor pressure of water. Without evacuation and introduced nitrogen following it, water vapor is much more difficult to remove and timely.
"Some always gets removed with the gas, and - along with moisture, sludge, and other contaminants "
If you are evacuating gas at a reasonable rate extremely little contaminates/sludge are carried along with the gas vapor., For it to carry contaminates the gas would have to to be causing a mist (fast boiling) within the system. Water vapor is readily carried with the evacuated vapor.
As to a micron gauge for $100, you might get lucky with a "mainland special". On the other hand I order (2) new Elitech gauges, both arrive DOA, first one had a slow leak, the second had a fast leak, Finally I purchased a Yellow Jacket, with a detachable vacuum sensor, which was leak free. Even the expensive gauges have a tendency to leak.
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I see a few listed on Amazon for $99 bucks. I have to imagine even the cheap micron vacuum gauges will give you a better idea of vacuum levels than standard analog manifold gauges. Plus, it's Amazon, they offer free returns if you're not happy with the product. (just don't wait longer than 30 days to send it back)