Vacuum range on HVAC gauge
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American Locomotive
Well-known member
You still need a micron gauge if you want to do the job correctly want a system that will provide years of reliable service.
motterpaul
Well-known member
I have to agree after a LOT of research that you need a micron gauge. A manifold gauge is like using a yardstick to measure millimeters (where did I read that)?
But the main reason for a vacuum is not to test for leaks - it is to purge the system of moisture and contaminants. If you don't know if you are getting a good vacuum you will never know if you really got your system ready for the coolant. That requires a micron gauge, IMO.
Also - nitrogen also blows out moisture and contaminants and exposes leaks. There are reasons for doing all this according to the recommended practices.
But the main reason for a vacuum is not to test for leaks - it is to purge the system of moisture and contaminants. If you don't know if you are getting a good vacuum you will never know if you really got your system ready for the coolant. That requires a micron gauge, IMO.
Also - nitrogen also blows out moisture and contaminants and exposes leaks. There are reasons for doing all this according to the recommended practices.
Milton Shaw
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Nobody else has mentioned this but all gauge sets I have seen have a zero adjustment screw under the glass. You can set the zero to any value you want. I have 4 different micro gauges and they vary readings by more than 50 microns hooked to the same manifold. If you get it under 1000 microns in the long run it's really not going to make a difference in the system as long as you have somewhere installed a dryer that will filter any water out of the oil. The smallest pickle dryer for refrigerators (about the size of a thumb) is rated to hold 100 drops of water so any residual moisture is not going to cause problems. I am not now a a/c professional but did work for GE and installed over 2000 refrigerator compressors in a 20 year career. Back then on R12 systems we didn't even use a vacuum pump or nitrogen purge on anything and recovery was not required until I had done about 1500 units. I did sweep with a puff of R12 and let the system pump itself down.
I know this is going to open a can of worms.
I know this is going to open a can of worms.
rlitman
Well-known member
It sure is. But the biggest one is that R12 used mineral oil, so it wasn't as affected by moisture as modern systems.
The dilemma was if it was the pump or the gauge si simply zeroing it out was n ot an option. BTW there was no screw but there was a hole if I remember correctly. I am no pro but I do wonder if the obsession with the microns is just that- an obsession. Is oxygen a problem too? Because yes, there are additional ways to handle moisture besides 500 microns of vacuum.
I would never rely on a gauge manifold to pull a vacuum. I always used a micron gauge. Back to the yardstick comparison. The gauge on the manifold will look like 30 inches at 1000 microns as well as 200 microns.
It would be like using a ruler to measure cylinder bores on an engine rebuild.
It would be like using a ruler to measure cylinder bores on an engine rebuild.
See, I am not an HVAC pro but there is something to be said about this yardstick notion. The point of using the regular gauge is to get some binomial assurance that the pump is working properly. The thinking is that a working pump will do the job. A perfect way of doing it for a NASA project? No. Could a reasonable person accept that as a feasible solution for a DIY-er? I think so. You can find (many) HVAC professionals who never use a micron pump. The manufacturers of DIY units do not require it. Not arguing, just advocating for a reasonable point of view that is out there.
danski0224
Well-known member
Fixed it for you.
As a DIY'er if you do an engine rebuld do you use a ruller to measure cylinder bores, or crank bearings? No, you find someone with the correct tools to measure, or buy them.
If a HVAC pro is not usimg a micron gauge he would get chastised by me. I was in the trade for over 20 years and I was using a micron gauge before it was cool, as it is the correct way to measure vacuum when you pump down a system.
Your "regular gauge" gives zero reference if the pump is working properly or if you are getting a proper, or even close vacuum. I have seen vacuum pumps that will pull 2000 microns that your gauge would indicate it is fine, or dirty oil in a vacuum pump that will not allow the pump to get anywhere close to the recommended vacuum.
If you want to half a** it, sure! The point is it is not the correct way. If you are satisfied with it, fine, but you are still doing it wrong. You still could have moisture in the system that will turn the compressor oil to acid and destroy it. A proper vacuum with a micron gauge will show that. And don't tell me it is a new system! I have poured water out of new sealed coils!
Can you measure .005" wear in a cylinder with a ruler? it is pretty much the same idea.
You can tell if you are getting vacuum, but not that last little bit that really makes a difference.
Personally, I have no clue why the AC gauges show vacuum, it is meaningless.
So you are not arguing, but it seems you are trying to justify doing it wrong. If the compressor fails in a year you will be wishing you had bought or borrowed a micron gauge.
Ah, what the heck, it will probably run for years!
American Locomotive
Well-known member
I wonder why you had to replace so many compressors over your career? GE's appliance division almost completely imploded in the late 80s and early 90s due to compressor failures, largely caused by poor decisions by management. So I'd say GE's refrigeration division didn't exactly make the best policies back then.
There are low-temperature and special systems where the low side may be in a vacuum while running. There are also systems where being pulled into a vacuum is part of normal operation - mainly walk-in freezer/refrigerator systems when they satisfy on temperature.
Well, certainly there are systems that run in negative, but how many guys ever work on one? Just a few percent. The far majority work on resi and commercial AC running R22 and R410.
American Locomotive
Well-known member
I'm not arguing about what most HVAC techs work on. Just that tool manufacturers sell their tools to everyone, so there is reason for them to read vacuum.
Snapped-off
Well-known member
firebirdparts
Well-known member
How high above sea level are you?
For people who live on land, there aren't actually 30 inches of vacuum available. That only works in the Navy or on the beach. That's the way it is.
For people who live on land, there aren't actually 30 inches of vacuum available. That only works in the Navy or on the beach. That's the way it is.
A few hundred feet above sea level but that's probably not an issue. -23" is very high.
On a single stage pump????? Would be VERY surprised to see that. Strongly suspect your gauge is not right. Just because something is digital and reads out to very high resolution does not in any way mean it is right. Digital stuff provides a very false sense of security.
Most my my vacuum systems work on really big things that need to get dried, and must also handle a lot of oil vapour. Oil changes are absolutely required for a deep draw - and anything needing to get much below 1 torr is going to involve a very large booster inline. I have good old fasioned absolute capsule gauges where I can to warn me of digital inaccuracy. My oldest is 45 years in service and still accurate and has triggered a half dozen digital replacements.
Back OT: the OP really needs to have a reference of either pump or gauge to compare what he has, no other way around it. Buying a new, digital absolute pressure gauge with a calibration certificate is a relatively safe and inexpensive way to be able to determine which one is wrong. We tried low buck refrigeration gauges as backups over the years, but in the end went back to the $1k range stuff as far more accurate and reliable - but not something that makes sense for a DIY operation.
metaldad
Well-known member
Yeah, like the typical service tech sees them every day!and r11, r113, r114
Jim greengo
Well-known member
I need to send out flyers to the owners of hundreds of ac's I installed in omaha/lincoln/bellevue/cb/louisville.........
In the last 30 plus years without a micron gauge.
And tell them all to wish their condensing units Happy Birthday from me. Hahaha
Jim greengo
Well-known member
I always thought 28" was perfect vacuam?
I can tell you about the "other" dealer in town that was constantly replaceing compressors in new units. The same brand we sold and almost never replaced a compressor. The Manager of the wholesaler had a quick meeting and asked us why we had so few warranty replacements and the other company did. We always used a micron gauge. He got back with us a few days later and found out they never did. He sold them a couple!
Your experience in the field maybe saving your ****. As for the OP and a rookie install, I wouldn't bet he knows how to ensure a system is tight and clean. Also new installs are generally easier to ensure they are clean and dry when they are put in. Coming back on someone else's hack install yo never now. You can not tell if a system is clear of moisture without a micron gauge. I mentioned before of the 5 ton HP that I had to pump for two days before the numbers fell in line. Previous techs just did a quick pump and dump, then can back in a couple years and did it again and charged the homeowner another $1,500. When I got done it ran for years.
As far as I am concerned, you have been lucky.
Jim greengo
Well-known member
I still come across r22 units from the 70s-80s from time to time,back before I was even the HVAC side of the business.
And they've some how managed to survive.
Long before anybody ever thought of needing a micron gauge on there van.
Not saying theres anything wrong with using 1 if you have it,but I get a little tired of everybody saying a condensing unit will not survive with out it.
The world is full of condensing units that were installed long before micron gauges were created,and they're still running.
danski0224
Well-known member
Those older units were more forgiving to improper installation practices.
I would also bet that more of those installations were done with some type of soft solder (whether it was Stay Brite or plain old 50-50 plumbers solder) compared to being brazed. I would guess that a bunch of **** in the lines from brazing without nitrogen is a bigger problem than not using a micron gauge.
I just pulled one out that must have had at least 20 elbows in it, all soldered with what looked like plain old 50-50 (it certainly wasn't brazed) and Type L water line with soft copper for the liquid line. Amazingly, the lineset (that term used loosely) seemed to be intact. The evap coil did have a hole in it.
R22 and mineral oil was more forgiving that R410 and POE.
15 years ago I replace the 30 year old R22 heat pump for my dad's house. The oil was bright green from acids in the oil. It was still running when I tore it out, but it doesn't make it right.
American Locomotive
Well-known member
...yah, and how many have died? The vast majority of those condensing units died, of the remaining ones, many are on their 2nd, or even 3rd compressor?
How many were condemned by coil failures/leaks due to acid/internal corrosion caused by poor evacuation?
You will always have survivors that defy the odds.
danski0224
Well-known member
Much like the person that condemns seat belts due to surviving an accident by being ejected through the windshield.
Jim greengo
Well-known member
If you get 30 years out of any heat pump,no matter what kind it is .
I'd say you should by some lottery tickets. Hahaha
mbunimog
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mbunimog
Well-known member
about done collecting tools to install the mini split. Just added the Bosch hammer drill to go through the 24 inch stone wall for the electrical connection. Lined it all up on the workbench
LS6 Tommy
Well-known member
You CANNOT use vacuum to leak test. I must post this 20 times a year here. Leak tests are under pressure with dry nitrogen.
Your hoses, valves, manifolds may not hold. I replace my hoses with HD charging hoses biannually. Critical equipment is evacuated with flared copper connections. All my valves are vacuum rated.
Tommy
You absolutely can if the objective is to check if your system won't hold vacuum due to a leak.
LS6 Tommy
Well-known member
I don't mean to sound harsh or condescending. You pressure test BEFORE you evacuate. Always. If you have an existing system that is flat out of gas, a vacuum pump is not the "go-to" for performing a leak check.
From now on I'll say "You cannot perform a SYSTEM INTEGRITY leak check with vacuum".
Tommy
You are absolutely right. Apples and oranges. The only reference to leak testing that you quoted was that a leak could not be the explanation why the system wouldn't hold vacuum. I.e it holds vacuum therefore it doesn't leak at vacuum. These DIY systems are not leak tested for integrity as that defeats the DIY part, Not required by the manufacture. You sure can if you want.
I don't mean to sound harsh or condescending. You pressure test BEFORE you evacuate. Always. If you have an existing system that is flat out of gas, a vacuum pump is not the "go-to" for performing a leak check.
From now on I'll say "You cannot perform a SYSTEM INTEGRITY leak check with vacuum".
Tommy
danski0224
Well-known member
Um, no.
danski0224
Well-known member
21, now...
Uh, yes.