Country of Origin: United States
I think I read a question by another person , about using a micron guage , on automotive A/C . But , either it was not fully answered or I did not comprehend the answer ?
On HVAC forums , it seems the use of a micron gauge is the " gold standard " for both commercial & residental HVAC ?
What say you all , for automotive A/C , and if possiable , could you also please share your reasoning ?
Personally, I use a micron gauge for my DIY auto a/c work. Once you start using one, you'll question every job you did prior :-) I ran into equipment leakage issues a lot when just starting out. My latest (and hopefully last) saga is related to the 4-port conversion I did on my manifold gauges. Using the micron gauge, I confirmed that some of the fittings were leaking as I was having trouble vacuuming down below about 1500 micron with nothing connected. The connecting hoses could EASILY pump down to 400 in a hearbeat. I'd used red loctite on the fittings, so I was surprised they were leaking, but they clearly weren't holding vacuum as well as I needed. You would NEVER have noticed this on your regular gauge set. If not identified and resolved, this would translate into an inability to vacuum the system down below 1500 micron. Generally, I like to pull down to 500 or so with the hope of stabilizing at around 750, although 1000 is deemed tolerable in my view, as long as it's holding rock steady there.
With all of these numbers I've just thrown out, you couldn't possibly register the difference on your gauge set. In the absence of a micron gauge, you resign yourself to pulling a vacuum for 45 minutes or so, and assuming the system pulls down real low. Waiting an hour or so is needed to allow enough leakage to be detected on the gauge set. With a micron gauge, I don't think waiting more than 15 minutes is needed. My experience has been that if I pull down to 500 and all is good, it will typically drift up to 750'ish within 3 minutes or less (or wherever it's going to hold steady). At that point, it will hold relatively steady for as long as you care to watch it. If there's a small leak, it either won't pull down to those levels or it will continue the upward drift without levelling out.
I have 2 micron gauges; a Robinair 14777 and a CPS VG-200. The Robinair unit has somewhat coarse resolution, albeit acceptable, for the application. The CPS unit would sometimes jump around in a manner that made me question the gauge. Until I built up confidence in using them, I tee'd off my low side line near the low side coupler and installed them in series to see how close the readings were. Doing this, I discovered that the CPS sensor needed to be cleaned off using rubbing alcohol when the readings jumped around. I believe it is related to getting oil or other foreign substances in the sensor. Once the sensor was cleaned, It's been rock solid ever since. Installing it in the tee and vertically ABOVE the flow helps to minimize the potential for contamination of the sensor. Although the VG-200 claims tolerance to positive pressure (not all micron gauges can tolerate positive pressure), I still valve it off when I go to charge or otherwise pressurize the system.
The thing I really like about using a micron gauge is that it gives pretty quick feedback as to your equipment setup. I've now modified my procedure such that after I get my manifold gauge set and charging hoses all ready to go, before attaching to the vehicle, I valve off the couplers and pull a vaccum on all the manifold hoses to ensure my equipment is capable of pulling down to the levels I expect (it won't hold at that level if you turn off the pump because there's too little volume to stabilize with the outside environment). With a 5 cfm vacuum pump, that should happen very quickly. If it seems to be struggling to pull down to those levels with such a small volume, it immediately tells me I need to double-check my equipment before hooking up to the system (where I'd otherwise have assumed an a/c system leak under such conditions).
In addition to rubber hoses, I actually investigated using coppper lines as well. My theory was that for the DIY'er, copper lines don't deteriorate from sitting in the garage for 6-12 months between uses whereas rubber hoses do, and are less likely to hold a good strong vacuum for long periods of time. I found that with copper lines, I WAS able to pull down a bit lower than rubber hoses, but not enough to matter for auto a/c purposes. I could get down to below 100 micron on the copper lines, whereas with my rubber hoses, I simply couldn't get much below about 250 (hoses are 4+ years old, only used a few times, but good quality ones). However, 250 is PLENTY for auto a/c work IMO. Plus, bending the copper lines to make connections is a PITA. I still think that rubber hoses are less capable of HOLDING a vaccum for a long time than copper lines, but I've since modified my setup to valve off the low/high side ports after the vacuuming period so there is no need for the hoses themselves to hold that vaccum indefinitely. Before the final charge, I'll vacuum out the manifold hoses again right before I charge just to be sure.
The obvious question that arises is that a/c systems use rubber hoses right? My only answer is that perhaps gauge set hoses are not of the "barrier" style to allow them to be a bit more flexible. Or maybe I'm just overly paranoid about pulling a vacuum :-)
Just my experiences, YMMV.
Edited: Thu July 25, 2013 at 11:59 AM by webbch
Thank you very much for the info / report . :-)
Do the micron gauges compensate for elevation ? Or is it necessary ? I am some what above 3,000 feet .
The vacuum measurement is relative to a perfect vacuum (which is what you're trying to achieve when vacuuming the system), not relative to ambient air pressure (like your gauge set), so no altitude compensation needed :-)
As a check, 14.7 psia is the atmospheric pressure at sealevel, right? At 3000 feet, it should be about 13.2 psia This corresponds to an absolute pressure of 26.875 in. Hg, or 682,637 micrometers of Hg, or microns. Thus, your micron gauge left open to the atmosphere (at 3000 feet) ought to read about 682,637 micron. I doubt it displays such a reading. My VG-200 stops displaying numerical values above about 25,000 micron.
If you read up on micron gauge usage, you only use the gauge on the vacuum pump to check the pump. They use a core tool with an extra connection point for the gauge and no manifold gauges till it's time to charge the system . They sell core tools with the extra fitting for 1/4" standard but not for R134A connection.
Only use a micron gauge to check the vacuum pump itself? To each their own, but I prefer to see what the A/C system is doing at high resolution under vacuum.
Furthermore, if one only uses a micron gauge on the pump, then you're back needing the hoses to hold vacuum over time. Whether the hoses contract slightly due to the vaccum, or if it's some kind of seepage effect, I do not know. However, I've noticed that newer hoses tend to "hold" vacuum better than older ones, and copper lines seems to hold vacuum the best. This observed behavior is what originally prompted me to investigate using copper lines. It's ultimately the reason I made the following contraption - to take the service hoses out of the loop when evaluating how well a vacuum is holding.
As you can see in the photo, it allows me to valve things off pretty close to the service port while keeping the micron gauge in the loop so that I can monitor vacuum loss. I also valve off the micron gauge when it's not needed for a particular operation.
I wasn't too clear. Correct, a micron gauge at/near the pump checks only the pump. Yes, you should be at/close to the system itself.
Not sure what one would do on a R134A system as I've never seen any kind of "tee" adapter yet? As far as that goes using a micron gauge for automotive A/C work isn't the norm.
For R134 systems, I use a Standard digital manifold with R134 scales. My miron guage fits on my standard core removers. At the end od my hoses (which are the heavy black vacuum rated hoses $$$$) I use the R12 to R134 adaptors.
I also will use no manifold, just my pump with a Yellow Jacket Tree on it with 3/8 black vacuum rated hoses with core removing tools. Then I adapt to R134 fittings. Sometimes depending upon the room access, I will use a manifold but only as a second choice.
Interesting. I don't quite understand what you mean by "my micron gauge fits on my standard core removers". Once I get hooked up and going, I prefer not to have disconnect hoses in order to change what I'm doing. If vacuum holds the way it should, I can switch right over to charging without disconnecting anything. Granted, when pulling a vacuum, that means a longer line because I have the vacuum pump attached to the 4th port on my manifold, and then it has to go to the low side service port via the manifold gauges. Lots of connections to leak - hence the reason I pull a quick vacuum just on the equipment setup before attaching to the vehicle to ensure it's up to the task.
If my only purpose was to pull vacuum, then I'd probably go direct from the vacuum pump to the low side port like you say, with the tee in the line right before it goes into the low side service port. That definitely minimizes the number of connections. In fact, I've done that with copper lines as part of my experiments to look at the difference between what my hoses will pull down to vs. copper lines (using an empty recovery tank as the test system to provide more volume than what the hoses can offer).
Edited: Fri July 26, 2013 at 6:00 PM by webbch
I don't own a micron gauge or core any tools but ran across this Video, although it isn't about automotive work, you'll see what I'm referring to. I admit to being a tool slut so heavens knows what's in my future!
Edited: Fri July 26, 2013 at 6:48 PM by wptski
Oh, I see how it works now. Thanks. Holy cow that was a fast evacuation. Couldn't tell what size vacuum pump he was using though. I used to remove cores to air up tires quicker, just never done it with a/c. I also noticed the size of those hoses. Dang! So THOSE are the ones for pulling down. Puts my regular service hoses to shame! I suspect copper lines are capable of similar performance, just subject to work hardening if used frequently.
Does copper get work hardened? I know brass does, I use to reload ammo. If it's the same just heat with a propane torch and dunk in some water to anneal.
To be honest, I've haven't TRIED to work harden the copper, I just suspect that if I bend it enough times it'll likely break. Given the infrequent use for a DIY'er, I don't see it as a major problem. But quite honestly, with my current setup able to pull down to 300 microns, that's good enough for me (for auto a/c purposes anyway).
I used to reload before Newtown (going on 8+ months now). I'd still be doing it, but now you have to give your first born child in order to get primers these days. It's very slowly getting better. I see now why folks stock up during the good times.
I sold all my reloading stuff years ago.
Here's an interesting thread about micron gauges: BluVac
Edited: Fri July 26, 2013 at 10:52 PM by wptski
Nice. If I didn't already have my VG-200, I'd probably go with that BluVac gauge. It seems to have been replaced by the UEI DMG200. Not sure if company was bought out in the last year or so. Anyway, the thing I like on it is the second part of the readout that tells you the leak rate. According to the manual, the time period used for the calculation is programmable - that's a nice touch.
Yeah, a micron gauge can be a double edged sword. On the one hand, it can really tell you what's going on with your equipment or the system once your equipment is "good". On the other hand, you really have to be careful in interpreting what it's telling you. It definitely has a learning curve, just like an electronic leak detector.
Most of my previous reading on micron gauges has been concerning mini splits .
I seem to remember reading on them , not to go much below 400 - 500 microns . At some point below that , the oil began to do funny things and changed enough to potentially loose some of its lubricating ( and possibly , other , beneficial ) properties ?
Any one else hear / read that ? Do not know it it applies to refrigeration oil in general ?
You can read about micron gauges till you go blind! What I find interesting and I've read before is that it's okay to have a vacuum leak as long as the rate isn't over a certain amount in a time frame. It's a pressure system not vacuum.
Yeah the BluVac shown in that video is slick but also not available at this moment due to manufacturer delay. It says mid July, duh?
If I get a micron gauge then check my ancient vacuum pump and it tells me that it isn't good enough then I need a new pump! I already have a few special tools that I've used but my never use again. I have a '78, '90 an '09 vehicle. The '78 is up for sale. The '90 I'm going to keep, I think. I'm working on its A/C now and first time touched in its lifetime. Waiting on a flex flare nut wrench for a evaporator fitting near the firewall.
Both Accutools(BluVac) and UEI show that same looking gauge other than color on their sites, wonder who really makes it?
I emailed Accutools yesterday and got an answer today, gosh on Sunday! They are the same, Accutool makes both, they partnered with UEI to broaden their distribution.
Edited: Sun July 28, 2013 at 2:06 PM by wptski
The lack of comments from members who are in the business leads me to believe that a micron gauge isn't used by them or overkill for automotive use.
Edited: Mon July 29, 2013 at 10:06 AM by wptski
We use them when needed, but it really is not as important to me as some. High quality vacuum pump with fresh oil is going to achieve a proper vacuum.
If they were cheaper , I would probably buy one , no questions asked .
I also work on my own HVAC , at home . Did I mention I am a brand new EPA card holder . :-)
I figure if I really need a micron gauge , I know enough technicians , I will be able to borrow one , perhaps at the price of a chicken fried steak ? :-)
Edited: Tue July 30, 2013 at 5:36 AM by WyrTwister
Agreed! I'd like to know how good or bad my old vacuum pump is but I might as well pass on the micron gauge and buy a new pump(maybe). If you do a search on VG you can read countless posts about people chasing equipment leaks. You need the best of everything, two core tools, one with a side port for the VG and Nylog on every fitting. They don't make a core tool with a side port for R134A fittings. Maybe a R12>R134A hose adapter would work but your adding another fitting and does one have the room for all this?????
What did you have to go through for your EPA card?
EPA card is simple - online test and get the card in the mail. I forget the fee involved, but it's pretty nominal as I recall. Really makes you question the whole "certification" process. Says NOTHING of one's ability to properly diagnose and repair A/C systems. It simply removes one's ability to claim ignorance regarding the venting of refrigerant into the atmosphere if the men in black ever show up.
Edited: Tue July 30, 2013 at 1:24 PM by webbch
There are several levels and categories . I took the open book version ( on line ) for the 608 Type I card . Cost about $ 25 .
All the other categories require closed book , with a proctor , I think .
As I mentioned , I have no plans to go into the business .
We've updated our forums!
Click here to visit the new forum
Copyright © 2016 Arizona Mobile Air Inc.