Optimum size Vacuum pump for Automotive A/C?

Hello everyone,

I’m a long time forum lurker, first time poster. I’ve been searching the forums and generally researching information, it really is a wonderful site, with masses of expert knowledge and experience.

Now I’ve buttered you all up I wondered if I could ask my first question that I can’t quite get to the bottom of by searching old posts, however I apologise if it has been asked and answered before but I have missed it.

As per the thread title: What would be the optimum sized vacuum pump for the evacuation of vehicle A/C systems?

After various readings, I've discovered the concept of too quick an evacuation causing the moisture to freeze rather than be removed.

I was about to buy a Javac 141 5CFM pump but now I wonder if this would be too large for vehicle applications and I'm worried it may freeze the moisture in the system rather than removing it as a vapour.

Could someone educate me please as to either an appropriate sized vacuum pump or a method for calculating/estimating the size of vacuum pump necessary for cars?

Thank you very much indeed for your kind help.

Regards
Mark

Go for their smaller pump but buy a good vacuum gauge.

You have to be carefull with the vehicles nowadays as many a different issue
1, modern vehicles hold next to no refrigerant some now only 325 grams nowadays so no massive issue there so small vac pump required
2, normally most vehicles have had multiple recharging so a good vac is no issue
3, modern cars use a slightly flammable refrigerant and it requires a special vac pump so u don't go bang
4, lots of vehicles now only have one test point
So providing it's a car and not a tank a twin stage 3 c f m with a digital torr gauge would do well I personally run a 8 c f m pump on vehicles as I do a lot of plant but you have one big advantage on vehicles you have a heater and a running engine to help heat the pipework evaporator etc and with o f n this sorts most moisture in a small amount on vehicles
Before its even vac ed ta charlie

Hello,

Thank you very much indeed to you both for your help and advice, I apologise for my delay in responding. From my searches of old posts, you both certainly know your stuff and are very experienced, you both come up quite a lot and I’ve already read a lot by you both.

That is really interesting and helpful Charlie. You must have been working on cars for quite a while, is that what you do, cars and plant?

So if I may go over a point in the original question – it’s about this business of moisture freezing with too quick an evacuation.

Though it is raised in other posts and discussions as something to be aware of, is it actually a reality? That is, does it actually happen in practice? Or is it only really with massively over-sized pumps evacuating relatively tiny systems? Charlie, I would have thought that if it was a real concern it would have given you big problems if you are using a 8CFM on vehicle a/c? I guess it hasn’t given you any problems then?

The thing is for just a little bit more money I can get a 5CFM size vacuum pump instead of a 1 – 3 CFM size pump. But then I don’t necessarily want to get equipment that is excessively over-sized or incorrect for my applications and that may cause me a problem.

Thank you
Mark

I wouldn't worry too much as you can only suck about 1.5cfm down standard 72" long gauge line.

My preference is the Robinair pumps as they have proven reliability and durability out in the field with us.
Any pump you should choose should be rated to 15/20 micron / millitorr on factory rating.
Always go the biggest pump you can, if you suspect high moisture in a system follow the triple evacuation method.
Pump ratings are in free air and at the low ranges your molecular flow is very low, so a bigger pump gets you there quicker (time is money) Then way up how heavy the pump is to transport and store and choose a sensible size for you!
Anywhere from 1 - 10 Cfm would be ok in your application, I would look at quality, reliability and replacement parts availability over size for small pump range.

Additional
We have a big pump on a trolley for the installation of VRF / VRV and industrial / large comercial plants and this is saving us a fortune in labour time evacuating big plants.

Quote:

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Originally Posted by charlie patt

3, modern cars use a slightly flammable refrigerant and it requires a special vac pump so u don't go bang
ta charlie

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Charlie I don't want to seem argumentative
the point you make though is pure sales rubbish from the salesman trying to get us to replace our pumps!
vacuum pumps are two stage vane pumps oil sealed with no real ignition source, even a sparking bearing is protected by lip seals and you would not be running your pump in this state with no oil.

When pulling a vacuum you are not pumping refrigerant, any refrigerant pulled out of the oil would be in an over rich state as air had been removed first and would not ignite (see point of ignition above)
amount of refrigerant would also be so small as to be purely theoretical.

If you have nitrogen purged before vacuum as we always should, where is the flammable refrigerant?

I must admit, i was thinking the same as hookster, if a job is done correctly then there will be no refrigerant in the system when proceeding to the vacuum stage due to recovery and purge of the refrigerant first

Quote:

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Originally Posted by monkey spanners

I wouldn't worry too much as you can only suck about 1.5cfm down standard 72" long gauge line.

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This is a genuine thought, not trying to be contrary, but if this is the case then does it mean then that the use of any pump greater than 1.5cfm is actually redundant?

What I mean is if I have a 5cfm pump vacuuming a system with hoses that limit the cfm to 1.5cfm, then presumably there's no benefit with such a size of pump?

What am I missing?

This guy has some interesting vids on vacuuming,

https://www.youtube.com/watch?v=hCXNL0IWb1I&t=711s

Some twin systems have solenoid valves well some are a bit more of a eev on suction and discharge if your vacuuming without vehicle running and climate on you will either vac half the system or when you run it and valves open up what ever is in it is now contaminated or worse if your on a modern crysler running 1234yf you pull ur vac you switch on vehicle to warm up switch ac on woops you now have 255 grams of slightly flammable entering your vac pump this is why with the modern equipment on vehicles you have to be carefull you assume ur system empty and it may not be this is where the flammable gas comes from and as far as the pumps go I seen what happens to a class terratrac when some knob vac ed it after assuming it was on 134 when it was on yf the new pump was the least of his issue vac ed it switched on ignition of combine heard the pump change noise then saw the flames come out by the time he got to it there was a lot of fire damage to his equipment and combine

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Vac pumps come in multiple sizes but mostly only 2 main types.

Single stage and two stage. What you need is a two stage with an interference between
stages, sometimes called a ballast or the ballast?? With the ballast screwed in the pump
works on both stages and pulls deep vacuum. With the ballast screwed out the first and
second stage get interfered with and it won't pull as deep, as quick. You then screw in
the ballast to finish off the deep vac.

As foe flammable gasses, the Hydro Carbon course (propane, butane and stuff) teaches
an exclusion zone of 3 metres form the vac pump to the electrical switch.

If you plug the vac pump into an extension lead and then switch the pump on and off at
the wall at least 3 mtrs away from the pump you can use any and all types of vac pump.

So a good vac pump with a ballast and an extension lead for switching flammables.......

Rob

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So what happens when the brushes flash on the armature shaft when the slip ring gets a bit worn ? I have vac pumps that vent on the handle just above the motor surely anything like this is a bit silly ? When dealing with these gases? Also a lot of these pumps have the three pin kettle plug so if it gets kicked whilst on in a localised area surely this ain't good practice, going back to the original question for cars nearly any pump will do with the wide range of cars out there it's hard to be accurate the problem you have is whatever you work on there is a vast chance some very unqualified people has already been at it ie Halford self fill so whatever pump you use will be no doubt better than most of what's been on it already I'm still a believer of having the correct kit for correct job and on whatever flammable gas I'm on i shall still be using the correct kit it's all well and good until something goes wrong and you can spend years building a good reputation and lose it in seconds ta charlie

.

The course teaches how to do it properly.

Why would you be vaccing a system with refrigerant inside?
The system should have been purged with OFN and possibly
pressure tested with OFN.

If the job is done correct there will be negligable amounts of flammable inside
and that is with propane or butain so the new A2L low flammable gasses would
be almost impossible to ignite.

Rob

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Thanks Monkey Spanners for the link, I did actually see your link in another thread while I was searching through older posts and they are a very good series of videos. It was a month or so ago and I must watch them again to see if it directly answers my original question, I can't quite remember, don't think it did though.

And thanks to the other replies too, its developed into a really interesting discussion with some valuable information contained in the replies

Rob the way u can have refrigerant in a vac pump is the new bmw crysler class kit run twin solenoids on twin and quad ac systems they two valves on a twin 8 on a quad totally isolate the pipes and evaporators on a twin or quad so on a 1234yf on a quad you reclaim refrigerant hp test then vac the problem being when you start car to warm cabin and switch on ac the solenoids open and approx 320 grams are heading for your vac pump the only way to open them is to energise ac or scanner so if your running a unsuitable vac pump it is surely possible things go bang if your using wrong kit it's going to end in tears this was my point in the beginning it depends what you work on but the days of popping a bit of gas into a modern vehicles is gone I'm afraid ta charlie

Quote:

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Originally Posted by charlie patt

Rob the way u can have refrigerant in a vac pump is the new bmw crysler class kit run twin solenoids on twin and quad ac systems they two valves on a twin 8 on a quad totally isolate the pipes and evaporators on a twin or quad so on a 1234yf on a quad you reclaim refrigerant hp test then vac the problem being when you start car to warm cabin and switch on ac the solenoids open and approx 320 grams are heading for your vac pump the only way to open them is to energise ac or scanner so if your running a unsuitable vac pump it is surely possible things go bang if your using wrong kit it's going to end in tears this was my point in the beginning it depends what you work on but the days of popping a bit of gas into a modern vehicles is gone I'm afraid ta charlie

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:D

The trouble with life is something always gets in the way and makes it complicated.

I agree there are always systems and circumstances that are designed or accident
that come along and disrupt normal procedures.

Good practices are good practices and informing people of systems like this is important.

You make good valid points Charlie and I was not trying to belittle them. The BMW sounds
like a dream to work on, you lost me at the first twin quad ..... :D

All the best Rob

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Calculation of Vacuum pumping capacity will require specification of internal outgassing rate or gas load at specified pressure and requested pump-down time.