A/C gauges vs micron gauges

[signcrafter]

I'm going to need to fill my A/C system after replacing a compressor. I'd like to buy the correct tools to do this myself. I have a set of mastercool gauges, http://www.amazon.com/dp/B00D2HTIIS/?tag=atomicindus08-20. The measure high and low side in PSI. In another thread a poster said you need to have a separate gauge/meter capable of reading less then 500 microns in order to charge an A/C system.

First question is can I charge an A/C system with a vacuum pump and the A/C gauges I have? Seems like most info on the web and youtube videos this is all they use.

If I have to use a micron gauge, what exactly does the micron gauge do and how is it used to fill an A/C system?

 

[RedneckWelder]

I was wondering about that too.

I'm going through an in depth vehicle A/C class for work now and all we use are normal gauges and normal A/C machines (which for our purposes basically combine vacuum pump, gauges, and an electronic scale in one). They did tell us that our charge has to be close to the specified weight for proper functioning, so we charge by weight from the scale.

When I charged my 134A system the other week on my personal truck all I used was a normal set of gauges, an old vacuum pump, and it works fine.

Maybe the newest refrigerant type (1234yf I think) needs these micron level gauges, I don't know. Don't deal with them in my field, we are mainly 134A.

 

[AA/FC]

A micron gauge measures vacuum in a much higher resolution than your typical anolog manifold gauge set. You do NOT need a micron gauge to recharge your automotive a/c system. It's just a gauge for reading vacuum..... it does not help achieve a lower vacuum, it just reads vacuum.

Micron gauges are typically used in commercial or residential a/c and refrigeration systems with sealed compressors. In automotive a/c systems, you typically connect your vacuum pump with your manifold gauge set and let it run.... the longer the better. Your vacuum level is read on you low side gauge and as long as your needle is near 29-30 inches, then you charge your refrigerant into the system. Done.

Very few guys use a micron gauge when charging automotive a/c.

Edit:

Short story......

Several years ago I completely rebuilt an A/C system in a chevy truck. EVERYTHING was brand new. Compressor, accumulator, condenser, evaporator, line set.... EVERYTHING was new. I also had recently bought a brand new Robinair vacuum pump and manifold gauge set. I decided since literally everything was new for this project that I would by a digital micron gauge to see how low I could get my vacuum level. After letting the pump run overnight, the lowest level was 770 microns.

After doing some research, I discovered there are MANY variables when connecting a micron gauge to your system. Hoses, quick connector o-rings, compressor shaft seal, altitude, barometric pressure etc,etc... ALL affect your achievable vacuum level. These guys who insist that you must reach 500 microns in an automotive A/C system before recharging are spouting off unrealistic numbers. When I do a system, if I can get down to 1000 microns I'm happy.

 

[BluByU]

Micron guage is for moisture. Let's you know much moisture is left while pulling your vacuum. Lower the number better off you are. I shoot for below 500 microns. A higher number will be less efficient and parts will where out faster.

 

[chris142]

I deal with people that tried to recharge there ac with gauges every day. IMO the best way is to start with an empty system.

 

[signcrafter]

I deal with people that tried to recharge there ac with gauges every day. IMO the best way is to start with an empty system.

As mentioned in first post it will be empty after changing the compressor. So you are saying an empty system charged with a set of AC gauges like I linked to in first post and a vacuum pump isn't good? Your post wasn't really too clear.

 

[AA/FC]

Micron guage is for moisture.....

A micron gauge is a vacuum gauge. It measures vacuum. It does not measure moisture. However, a lower vacuum level indicates low moisture levels.

 

[Ruger_556]

After doing some research, I discovered there are MANY variables when connecting a micron gauge to your system. Hoses, quick connector o-rings, compressor shaft seal, altitude, barometric pressure etc,etc... ALL affect your achievable vacuum level. These guys who insist that you must reach 500 microns in an automotive A/C system before recharging are spouting off unrealistic numbers. When I do a system, if I can get down to 1000 microns I'm happy.

International says 1000-750 microns. That's what I roll with...

 

[Anarius]

If you have opened the AC system, you need to either buy all the tools to do it right or take it to a pro. A/C recharges are not expensive. I think we get $70 incd the 1st lb and $25 for each additional.

The little cans you can buy are for topping off, and even that is stupid.

Your A/C system is rated and designed for a specific WEIGHT of refrigerant, the only way to get that right is with a scale. If you go off pressures, you can sorta maybe kinda get close. Many factors can affect the gauges, like ambient temperature, engine and HVAC heat loads, wear and tear on compressors, evap devices, small restrictions in condensers and other parts....blah blah blah.

Also, when you expose the system to air, you introduce moisture, which needs to be removed or it can form ice. Also, air in the system takes the place of some of your refrigerant charge, lowering the overall performance. The system should be vacuumed for at least 30 minutes if it was left open for a significant period of time, a minimum of 10 minutes all other times. Not to mention vacuum leak tested for another 10 minutes afterward.

With the system empty, you must use the pressure in the cans to force the refrigerant into the low side of the system, and have to get at least a 1/2 lb before most compressors will kick on. You will find that the can runs out of "oomph" long before that happens. You can either waste the remainder of the can, or force the compressor to run by bypassing the low pressure switch. Which can cause damage, especially on nice shiny new ones.

Oh, and don't forget your oil...

 

[Lx460]

What kind of vacuum pump determines how long you need to evacuate the system. The vacuum lowers the boiling point of the moisture in the system so it boils off at ambient temperature and out the vent on the pump. Sometimes you can see it.

Any time your system has been opened for a period of time, you need to replace the dryer/accumulator. It has a desiccant inside that absorbs moisture. If open for any significan amount of time it will absorb moisture from the air and no longer work properly.

If you have the time, leave the gauges hooked up and see if they hold the vacuum. If they do, it's likely you repaired the leak. It also makes it easier to add refrigerant with the system under vacuum. Just find out what you system capacity is and if using cans they are typically 12oz. each. If you have a larger cylinder, you will need a scale to properly measure it. When you add the refrigerant, have the vehicle idling with A/C on max , high fan speed. Also only charge through the low side port (blue hose).

 

[signcrafter]

With the system empty, you must use the pressure in the cans to force the refrigerant into the low side of the system, and have to get at least a 1/2 lb before most compressors will kick on. You will find that the can runs out of "oomph" long before that happens. You can either waste the remainder of the can, or force the compressor to run by bypassing the low pressure switch. Which can cause damage, especially on nice shiny new ones.

Oh, and don't forget your oil...

So if I vacuum the AC system down using a vacuum and set of gauges the cans will loose "oomph" before it can start to charge?

 

[Lx460]

So if I vacuum the AC system down using a vacuum and set of gauges the cans will loose "oomph" before it can start to charge?

If you have the system under a vacuum, you will be fine. If you try to add the cans to a closed system that has not been under vacuum, you may have a issue.

Most systems only use around 3 12 oz. cans. Except for some large SUVs with rear A/C. There's no need for a 20 lb. cylinder and scale for home use. Check your capacity to be sure. Should be a sticker under the hood or look it up online. Also as pointed out before, make sure your new compressor has the correct amount of oil in it already or it won't last very long. Some come pre-filled, some don't. I usually dump out whatever is in there when shipped and re-measure according to the required amount.

 

[AA/FC]

So if I vacuum the AC system down using a vacuum and set of gauges the cans will loose "oomph" before it can start to charge?

It's possible that there won't be enough pressure in the can to fill the system enough to trigger the low side switch, which is what engages the clutch on the compressor. If this happens, you can jump the low side switch until the system gets enough refrigerant for it to operate properly on it's own. Remember, the compressor does not "****" the refrigerant into the system..... it lowers the low side pressure in the system, which allows the higher pressure in the can to "push" the refrigerant from the can into your system.

 

[Lx460]

There are also some other variables involved with automotive A/C. If your compressor "grenaded", you will likely also need a new condenser as it is impossible to flush out the debris. Also as I said before replacing the drier is almost mandatory (for me anyways) when replacing a compressor. Depending on the vehicle, I'd also replace the orifice tube/expansion valve while I had the system open.

 

[signcrafter]

It's possible that there won't be enough pressure in the can to fill the system enough to trigger the low side switch, which is what engages the clutch on the compressor. If this happens, you can jump the low side switch until the system gets enough refrigerant for it to operate properly on it's own. Remember, the compressor does not "****" the refrigerant into the system..... it lowers the low side pressure in the system, which allows the higher pressure in the can to "push" the refrigerant from the can into your system.

I thought this was the whole point of vacuuming the system down. So the vacuum will "****" the refrigerant into the system. But you are saying even if you vacuum the system down it won't **** the refrigerant into the system?

There are also some other variables involved with automotive A/C. If your compressor "grenaded", you will likely also need a new condenser as it is impossible to flush out the debris. Also as I said before replacing the drier is almost mandatory (for me anyways) when replacing a compressor. Depending on the vehicle, I'd also replace the orifice tube/expansion valve while I had the system open.

I ordered the compressor, drier, and orifice tube from rockauto.

 

[Lx460]

I thought this was the whole point of vacuuming the system down. So the vacuum will "****" the refrigerant into the system. But you are saying even if you vacuum the system down it won't **** the refrigerant into the system?

It will take it via cans, you'll be fine.

 

[signcrafter]

It will take it via cans, you'll be fine.

Thanks

 

[AA/FC]

I thought this was the whole point of vacuuming the system down. So the vacuum will "****" the refrigerant into the system. But you are saying even if you vacuum the system down it won't **** the refrigerant into the system?

The whole point of vacuuming the system is to remove air and moisture. Most importantly moisture!

And yes, the vacuum will **** the refrigerant into the system...... for about the first 10 seconds.... until pressurized refrigerant overcomes the vacuum and the system is no longer "in a vacuum". At this point you need the compressor running which will keep the low side pressure lower than can pressure. It's all about pressure differential..... As long as the compressor keeps the low side pressure in the 28-40 psi range, it will allow the pressure in the refrigerant can (about 85 psi at 80 degrees) to push the refrigerant into your system.

If your compressor shuts off, and your system pressure equalizes (again, about 85psi at 80 degrees) then no refrigerant will flow from the can to your system. It can't if the system pressure, and the can pressure is the same.

 

[AA/FC]

I don't normally post other forums, but you might want to take a look at this one. It's obvious that A/C work is fairly new to you and this forum is great for beginners. Literally ever question that can possibly be asked has already been covered on this site:

http://www.acsource.net/acforum/viewforum.php?f=1

 

[joel63]

A micron gauge measures vacuum in a much higher resolution than your typical anolog manifold gauge set. You do NOT need a micron gauge to recharge your automotive a/c system. It's just a gauge for reading vacuum..... it does not help achieve a lower vacuum, it just reads vacuum.

Micron gauges are typically used in commercial or residential a/c and refrigeration systems with sealed compressors. In automotive a/c systems, you typically connect your vacuum pump with your manifold gauge set and let it run.... the longer the better. Your vacuum level is read on you low side gauge and as long as your needle is near 29-30 inches, then you charge your refrigerant into the system. Done.

Very few guys use a micron gauge when charging automotive a/c.

Edit:

Short story......

Several years ago I completely rebuilt an A/C system in a chevy truck. EVERYTHING was brand new. Compressor, accumulator, condenser, evaporator, line set.... EVERYTHING was new. I also had recently bought a brand new Robinair vacuum pump and manifold gauge set. I decided since literally everything was new for this project that I would by a digital micron gauge to see how low I could get my vacuum level. After letting the pump run overnight, the lowest level was 770 microns.

After doing some research, I discovered there are MANY variables when connecting a micron gauge to your system. Hoses, quick connector o-rings, compressor shaft seal, altitude, barometric pressure etc,etc... ALL affect your achievable vacuum level. These guys who insist that you must reach 500 microns in an automotive A/C system before recharging are spouting off unrealistic numbers. When I do a system, if I can get down to 1000 microns I'm happy.

You understand the principle of evacuation very well.
There's a lot of bogus information out there.
Check out the steam and water tables and look at the boiling points at the various temperature and pressure (vacuum) levels

 

[joel63]

The whole point of vacuuming the system is to remove air and moisture. Most importantly moisture!

And yes, the vacuum will **** the refrigerant into the system...... for about the first 10 seconds.... until pressurized refrigerant overcomes the vacuum and the system is no longer "in a vacuum". At this point you need the compressor running which will keep the low side pressure lower than can pressure. It's all about pressure differential..... As long as the compressor keeps the low side pressure in the 28-40 psi range, it will allow the pressure in the refrigerant can (about 85 psi at 80 degrees) to push the refrigerant into your system.

If your compressor shuts off, and your system pressure equalizes (again, about 85psi at 80 degrees) then no refrigerant will flow from the can to your system. It can't if the system pressure, and the can pressure is the same.

Yes, Yes, Yes.

 

[chris142]

Ya I posted 1/2 asleep. Start with an empty and vacuumed system and charge by weight. Gauges will help but by weight is preferred as theres too many variable. Every type of car holds a different amount.look for a sticker on yours and don't over or under charge it

 

[signcrafter]

So AC gauges just tell you the high and low side pressure inside the system right? Micron gauges measure the vacuum the system is under when you hook up your vacuum pump? And scales are used to measure the exact amount in weight of refrigerant that you are putting in your system?

So in theory you hook up a set of manifold gauges to access the system. The PSI reading can be good for troubleshooting AC issues but isn't really accurate for filling the AC system? To fill an AC system you need a to pull a vacuum and measure it with a micron gauge/meter? Then to add the refrigerant you need a scale to measure the exact weight of the refrigerant that goes in?

Am I understanding the differences in the tools and what each one does and why you need each one?

 

[Davefr]

Anyone that doesn't get down to the specified micron level is a "hack". Usually around 500 microns.

...and how do you know if you're getting there if you can't measure it?

99% of manifold gauges won't measure this low. There are exceptions but they're expensive.

The only exception to this would be the triple evac. method where you vacuum then let the system **** in dry nitrogen and repeat about 3 times. The nitrogen helps dry out residual moisture in the system if you can't achieve 500 microns.

 

[signcrafter]

My gauges don't measure microns at all I don't think. Just PSI for high and low and then on the low side has a hg scale. So I have a set of manifold gauges and ordered a vacuum pump. I still need a micron gauge and scale right? What would be a decent micron gauge for occasional home use?

 

[Davefr]

My gauges don't measure microns at all I don't think. Just PSI for high and low and then on the low side has a hg scale. So I have a set of manifold gauges and ordered a vacuum pump. I still need a micron gauge and scale right? What would be a decent micron gauge for occasional home use?

Maybe a Fieldpiece digital vacuum gauge and use a cheap digital postal scale with tare function.

Try and perform a dry run before working on the actual system. Getting down to 500 microns can be pretty unforgiving to cheap hoses and leaky fittings.

 

[royesses]

Note! Always wear safety glasses when working around refrigerant!!!
To explain a little about the micron gauge use you should realize that water boils off at a temperature that is determined by the pressure it is at. But it does not instantly go away. If you place a pot of water on a stove and heat it, it takes time to reach its boiling point temperature depending on the altitude of your location. The altitude I am at is 1210 feet above sea level and water boils at 210 degrees F. When it reaches the boiling point the water consumes a massive amount of heat (btu's)to convert to steam. It is boiling, but the water is still there. In other words it takes time to boil the water off so that the pot no longer has any water in it. The more water, the longer it takes. In a closed system when the water starts to boil the pressure rises as the water is boiled off. A standard manifold gauge set doesn't have the resolution to see this. A micron gauge does. The micron reading will go down until the water in the system starts to boil, say to 700 microns. Then the reading will climb to say 1000-1400 microns. This is the water converting to steam and raising the pressure. As the vacuum pump continues removing the water the micron gauge reading will get lower. This may happen multiple times until the water is completely removed. When that happens the micron gauge will reach a lower and lower reading until it reaches the highest vacuum the pump can produce. With my pump it is about 400 microns. I leave the pump on for about 15 minutes after that.

So the micron gauge allows you to see the moisture in the system being removed. If there is no moisture in the system the micron reading will steadily decrease until maximum vacuum is reached and will stabilize. Any leaks in the system or manifold/hoses will prevent a low reading.

Also the vehicle manufacturer places a label telling you the optimum charge for the vehicle in the engine compartment. Your hoses and manifold will contain some refrigerant so you need to compensate for this by adding 1 or 2 oz. of refrigerant more. There is a way to measure when the system is at optimum charge using superheat readings. Most automotive shops don't bother with that. http://acsource.net/acforum/viewtopic.php?f=1&t=4670&p=20113

Most commercial A/C shops use scales with a heater to speed up the process of filling the system. Using the small cans I get a 5 quart pot of water at 90 degrees F and swirl the can in it when charging the system to help speed up the process. It is important not to get the water hotter than this or you will stand to create a hydraulic hand grenade.
Some links with further information:
http://www.aircondition.com/tech/questions/95/Basic-Charging-Procedures
http://yarchive.net/ac/vacuum_pumps.html
http://aircondition.com/tech/

 

[Lx460]

Anyone that doesn't get down to the specified micron level is a "hack". Usually around 500 microns.

...and how do you know if you're getting there if you can't measure it?

99% of manifold gauges won't measure this low. There are exceptions but they're expensive.

The only exception to this would be the triple evac. method where you vacuum then let the system **** in dry nitrogen and repeat about 3 times. The nitrogen helps dry out residual moisture in the system if you can't achieve 500 microns.

The guy is trying to repair the a/c in his vehicle not build an intergalactic transwarp space vessel.

He doesn't need to measure microns.

He doesn't need a bottle warmer.

He doesn't need a scale.

He doesn't need to flush the system with Nitrogen.

You guys are making such a big deal out of this...

Vacuum it down for an hour, longer if you want to.

Start the car, fill it with the cans.

If you did a good job putting everything back together and don't have any leaks...

DONE.

 

[Davefr]

The guy is trying to repair the a/c in his vehicle not build an intergalactic transwarp space vessel.

He doesn't need to measure microns.

He doesn't need a bottle warmer.

He doesn't need a scale.

He doesn't need to flush the system with Nitrogen.

You guys are making such a big deal out of this...

Vacuum it down for an hour, longer if you want to.

Start the car, fill it with the cans.

If you did a good job putting everything back together and don't have any leaks...

DONE.

Modern HVAC systems are very unforgiving to "hack" jobs. The devil's in the details.


Do it the right way or take it to somebody that will.

 

[Pwaley]

Necro-bump.

Sounds like some folks shouldn't be giving their two cents if they don't have any professional or even remote experience in HVAC/MVAC work. From what this video is showing me, 30" of Hg don't mean anything other than you are pulling a vacuum and or are holding it. Do it once, do it right or don't do it at all. Ain't that what your mammy or pappy taught you?!

Now to hunt for a quality but <$200 micron gauge. Supco? YJ? CPS? I really want the YJ 69075 but that is a pricey son of a gun for home MVAC use!


Go to the six (6) minute mark.
https://www.youtube.com/watch?app=desktop&v=nBCWYgCcnpE

Here's another pro explaining the importance of a micron gauge and not just going by an arbitrary amount of time as well as going off of the crude 30" of Hg hold. Go to the 18 minute mark of this video. I believe he is 40 minutes in of vacuuming and the micron grade is still >2500!

 

[Milton Shaw]

If removing moisture is the goal then the answer is a new dryers. Even the smallest dryer will catch/remove an amazing amount of water. I did refrigeration repair for 20 years for GE. Replaced 2,000 compressor under a recall. We never used a vacuum pump, and these were systems that only held 4 to 7 OZ of R12. The pickle dryers we used were about the size of a thumb and would handle 100 drops of water. Never any problems with air, moisture etc. I am still using one 35 years after I installed the compressor. Conventional hoses, fittings, seals, gauges leak enough so that micron gauges won't read accurate. Old oil in vacuum pumps will also affect the readings. If you don't think so just hook micron gauge directly to pump and run for 30 minutes and then change oil and run it 30 more. Hook up your hoses and dead head them to the manifold and read microns again and see what hoses/gauges are doing. In super critical work in vacuum chambers in labs the total vacuum is read at a whole lot less than one micron. That is not needed in normal a/c work. Normal R134 hook ups leak enough to give bad readings if you are looking at microns. Yes excessive moisture is a problem but the new dryer/receiver change will take care of it unless someone has flushed system with wet compressor air and even then the dryer will handle it. This is over 40 years experience and over 2,000 compressor swaps on a/c's and refrigerators. I know this is going to raise a lot of comments but this has been my experience. I do now have micron gauges, electronic scales, vacuum pumps and use them when charging systems but 40 years history have taught me that it works either way 99 % of the time.