Auto A/C vacuum pump. lots of CFM or Less CFM whats best?? A/C tech's please help.

Nasty-LSX · Jul 6, 2024

I am going to buy a A/C vacuum pump for auto/truck. They have so many options when it comes to CFM.
from 3.5 to 9.5. is the highest # the best to have. Its obvious the higher the CFM the more $$$$$ the unit is.
Im not a HVAC tech so I dont know is CFM matters or not, other wise im going to buy this unit. Whats your thoughts.

https://www.amazon.com/SPECSTAR-Economy-Vacuum-Pump/dp/B09KBJS36B/ref=pd_ci_mcx_pspc_dp_d_2_t_2?pd_rd_w=sesLT&content-id=amzn1.sym.568f3b6b-5aad-4bfd-98ee-d827f03151e4&pf_rd_p=568f3b6b-5aad-4bfd-98ee-d827f03151e4&pf_rd_r=G0GHV1N477GZGDZH6FBT&pd_rd_wg=cLvrF&pd_rd_r=a16903a1-cc7b-4599-a367-5caaa5e799a3&pd_rd_i=B09KBJS36B&th=1

RanchWelder · Jul 7, 2024

Elevation makes a difference.
Former A/C tech. Repaired microwaves.
Studied Multi-Channel microwave coms too.
512 Universe DMX programming systems for moving lights.
Personally wired 8-12 Universe lighting systems for corp symposiums.
IBM 14 years.

5 cfm pump will not pull 25 HG at 5000 ft.
7cfm might be required to maintain 25 cfm above sea level.
2.5 or 3 is not recomended.

You live on/near the beach.

Should have bought 9 cfm for mile high altitude.
It works and I get 22.5 cfm, which works OK for my use.

Go 7 cfm and be certain you actually get what you expect from a $$$ investment, IMHO. Remember leaking seals will never pull full cfm. The colored die works for leak checking seals. If you want A/C you need to die the system for leaks, OK?

AZ sold and delivered will cover your risk, if you ask politely to return whatever you buy. Try the Wearhouse Dealz?

Here's what I paid $112 for on an AZ flash sale: Vevor 7 cfm, with extra fittings and valve shut off features.

https://www.ebay.com/itm/364929148193?epid=17068697828&itmmeta=01J261AXGZQR5ZKR54X6EVN05H&hash=item54f778e521:g:CWAAAOSw3pZmYwYs&itmprp=enc:AQAJAAAAwMlOHa3+X7bjmL8ofXwzMGpoPxP7gnKfyqmHe1RLW3+7DXS5Y5DWPRr5a6OIj8limlYcFNybMDbHGLc0Vl/7zMgYOyb0HOZFKrYS+EM0QaduLYoRCiUkNWCRAy3jDJiBq2Br+lRrDRW7LtirDHlPm9UXe5KEgYJRPVl/xLM/xIyeNQzoQIHohxqBcqQ39iR/5aE6kdLhXRdAQM+7HOXC58jtwKRRqw910ZDPdfFnc6kQx96px1nIbZlf7LJbg/UW9Q==|tkp:Bk9SR8rYq8GRZA

I'm really pleased it was so cheap and seems to work OK at elevstion with minimal hg loss. Similar units on AZ are double the price now and this unit is no longer for sale?

Mine came with 2 bottles of oil for the compressor. You'll need them too.
See if this seller will ship you the pump and the 2 extra bottles of oil at the same time. They come packed with special foam for the bottles included. Good box, excellent foam for safe delivery. All the extra fittings. The box is really good for future storage, if you don't have bench space.

AZ is raising seller's pricing requirements, so you might be better off buying from ebait for the next few months on special order items from overseas suppliers.
Rocket engines are damn expensive.

Just remember to pull the black plug/stopper before you fire it up.
(Same with your rocket engine supply lines?)
Anybody can forget to pull the safety plug on a rocket engine, right?

It keeps the oil free from dirt, and needs to vent to pull vacuum without damaging the pump.

YMMV

Nasty-LSX · Jul 7, 2024

Awesomeness man, thank you so much. Great info. I'm in south Texas 60 miles from the gulf. I don't think I'm in high elevation. I wanted the one I posted cause it's a higher # for CFM. I am to get into HVAC residential and commercial, but wanted a vacuum that I can use on cars also. I don't have a problem with price. So I'm assuming the 9 CFM is adequate enough? Thanks again :favorites13:

CheemsK1500 · Jul 7, 2024

ETA: misread the thread title and thought we were talking about vacuum pumps to replace intake vacuum sources.

RanchWelder · Jul 7, 2024

Verify the pump works ASAP, is my best advice.
This is not really a professional unit like you would find at Grainger.
Few A/C charges a year and some bench time for a transmission rebuild for Valve Body testing, like shows in his videos, is why I opted for this version.

If you are serious about A/C work, I would bite the bullet and cough up the $600 for a quality service unit from your local Air Conditioning Supply Warehouse.

They will not even sell you R-12, R22, bulk R-134, unless you start an account and buy the regulated HQ equipment. Most places require certification and a business license in good standing to open an account for any gas sales.
They will know if you do not have credentials.

The small commercial cans are cleaner than the crap you buy off the shelf.
Any can with a plastic gauge on the top might be contaminated from the factory.
They don't wash the cans during manufacture.
Aluminum, dirt, toxic waste?
No telling what's in a can running at 100 mph in a foreign bottling factory.

The good stuff is worth the time to acquire, so you do not ruin a high dollar system.
Posted similar recommendations at GMT400.

If you gamble with contaminated gas, be ready to change the orifice in the very tough to get spot on your condenser. If the oil gets contaminated, you'll be purging to clean the crap out before it will run the way it did from the dealership, in many cases.

Same advice as my fuel systems advice: New quality OEM O-Rings Everywhere...

fast 99 · Jul 7, 2024

An acquaintance who owns a used car lot bought some cheap supposedly virgin refrigerant. Sealed in the box. He ended up replacing entire ac systems on every car that got some of it from corrosion.

Hunter79764 · Jul 7, 2024

On bigger systems (i.e. residential and commercial HVAC instead of automotive) more CFM = less time to evacuate/pull vacuum. Like welder said above, a minimum size is needed to actually work practically, but basically the bigger the better, all things even. Auto systems occasionally doesn't matter too much. When there's a time requirement, you need to consider what your time costs you and costs the customer and buy your tools accordingly.
That unit looks like a reasonable good deal, good reviews etc. And more CFM will do the same job quicker, easier, and/or to a deeper vacuum, so buy what you can afford, there's no "too much" on it for most typical purposes. My usual approach on specialty tools I don't have experience with, is to buy one that is reasonable mid-level. By the time it wears out, I know what I'm looking for, know what I'm willing to pay, and know what other folks are using and having good luck/trouble with and then decide what I'm going to buy for a "forever tool". If it doesn't wear out or continues to be servicable for my needs, I didn't have to pay the big bucks for the "name brand", and if it fails, it was worth the money to learn. Bonus if you get to a point that you know what you want and the old one still works, then you have a useable backup. And vacuum pumps do have a tendency to get left on a job site (maybe pumping down overnight, then have a quick job to hit the next morning before going back to the regular site?).

All that said, note that I'm not a tech, I haven't made my living off of it, but I was a design engineer for Lennox in the past and worked with some talented older technicians that I did my best to learn from.

SquareRoot · Jul 8, 2024

This thread sucks

Trucksareforwork · Jul 8, 2024

SquareRoot said:
This thread sucks

Yeah, but how much does it suck? It doesn't sufficiently suck until it hits 29in hg.

Trucksareforwork · Jul 8, 2024

I'm sitting at about 1000 above sea level and have had one of the 3 CFM harbor freight units for a few years. It pulls down to about 29 in at least based on my gauges. I think it's the 3CFM ("2 stage") one.

Bextreme04 · Jul 8, 2024

RanchWelder said:
Elevation makes a difference.
Former A/C tech. Repaired microwaves.
Studied Multi-Channel microwave coms too.
512 Universe DMX programming systems for moving lights.
Personally wired 8-12 Universe lighting systems for corp symposiums.
IBM 14 years.

5 cfm pump will not pull 25 HG at 5000 ft.
7cfm might be required to maintain 25 cfm above sea level.
2.5 or 3 is not recomended.

You live on/near the beach.

Should have bought 9 cfm for mile high altitude.
It works and I get 22.5 cfm, which works OK for my use.

Go 7 cfm and be certain you actually get what you expect from a $$$ investment, IMHO. Remember leaking seals will never pull full cfm. The colored die works for leak checking seals. If you want A/C you need to die the system for leaks, OK?

AZ sold and delivered will cover your risk, if you ask politely to return whatever you buy. Try the Wearhouse Dealz?

Here's what I paid $112 for on an AZ flash sale: Vevor 7 cfm, with extra fittings and valve shut off features.

https://www.ebay.com/itm/364929148193?epid=17068697828&itmmeta=01J261AXGZQR5ZKR54X6EVN05H&hash=item54f778e521:g:CWAAAOSw3pZmYwYs&itmprp=enc:AQAJAAAAwMlOHa3+X7bjmL8ofXwzMGpoPxP7gnKfyqmHe1RLW3+7DXS5Y5DWPRr5a6OIj8limlYcFNybMDbHGLc0Vl/7zMgYOyb0HOZFKrYS+EM0QaduLYoRCiUkNWCRAy3jDJiBq2Br+lRrDRW7LtirDHlPm9UXe5KEgYJRPVl/xLM/xIyeNQzoQIHohxqBcqQ39iR/5aE6kdLhXRdAQM+7HOXC58jtwKRRqw910ZDPdfFnc6kQx96px1nIbZlf7LJbg/UW9Q==|tkp:Bk9SR8rYq8GRZA

I'm really pleased it was so cheap and seems to work OK at elevstion with minimal hg loss. Similar units on AZ are double the price now and this unit is no longer for sale?

Mine came with 2 bottles of oil for the compressor. You'll need them too.
See if this seller will ship you the pump and the 2 extra bottles of oil at the same time. They come packed with special foam for the bottles included. Good box, excellent foam for safe delivery. All the extra fittings. The box is really good for future storage, if you don't have bench space.

AZ is raising seller's pricing requirements, so you might be better off buying from ebait for the next few months on special order items from overseas suppliers.
Rocket engines are damn expensive.

Just remember to pull the black plug/stopper before you fire it up.
(Same with your rocket engine supply lines?)
Anybody can forget to pull the safety plug on a rocket engine, right?

It keeps the oil free from dirt, and needs to vent to pull vacuum without damaging the pump.

YMMV

CFM rating has nothing to do with how much vacuum you can pull with elevation. Vacuum is read as a gauge pressure relative to atmospheric pressure. Atmospheric pressure is ~29.92 inhg at sea level and drops ~1inhg per 1000ft in elevation above sea level.

The CFM rating tells you how fast the vacuum will be pulled. Since it is a sealed system, you are not trying to overcome any air coming into the system, so CFM rating doesn't affect ultimate vacuum level. There should also be a rating on the pump called "Ultimate Vacuum". That rating will tell you what you should be able to expect from a final vacuum reading once it has pulled the system down. I have a 3.5cfm one I bought in 2017 on amazon and it has an ultimate vacuum rating of 5Pa. So it can pull vacuum down at 3.5 cubic feet per minute of atmosphere down to a total vacuum of 0.000295 inhg of ambient atmosphere on the gauge(so close to ambient you shouldn't be able to tell on the gauge).

RSMII · Jul 8, 2024

I had my own a/c business back in the late 80's and I had a 5cfm 2 stage vacuum pump. It worked well for everything from commercial systems to auto a/c. I'm at 1000' altitude. If your not at any high altitude in Texas (I think that area is kinda flat) 5cfm 2 stage will work fine. Is bigger better?, it doesn't hurt. Unless you plan on doing massive commercial systems 5cfm is good. I still work on auto a/c systems and still use a 5cfm vacuum pump.

RanchWelder · Jul 8, 2024

RSMII, Your 1980's pump is probably not the one from Ebait for $89 made in China, is it?

At 5000 ft, the transmission test manual states the vacuum potential will be less due to elevation, "AT THE RATED HP OF THE ELECTRIC MOTOR". ...and it is.

Now imagine the Chinese gentleman who rated the "7 CFM" and designed the "SUPPOSED" 1/2 hp electric motor, cut corners, used thin sort of copper windings, made a fib about rated cfm and actual power at sea level, used cheaper non efficient components and bearings and a leaking pump vane assembly and had a farm boy fresh from the country fields to assemble it?

So max potential vacuum on my cheapo faker vacuum unit is a lie, from the day it was made.
It's not 1/2 hp either.

Nahhh, they would never do that...

___________________________________________________

Why I suggested you go to Grainger Supply and buy the heavy duty professional unit if you intend to do professional A/C systems and require real world numbers and quality bearings/windings.

The one for sale cheap on ebait might not actually produce the rated hp or cfm, which why it is open box on sale?

You get what you pay for. There is no free lunch.

Hang in there Nasty-LSX, it's going to get windy with lot's of rain down there... with Beryl in town.
We're all rooting for you!

SquareRoot · Jul 8, 2024

I'm gonna agree with Bextreme04 on this. I get the logic of vacuum being less in thin air at the same HP but..... you're confined to a sealed system. The ambient air pressure doesn't matter. Now if you are compressing air it's a different story. Then you'd need to turbo that baby! Think about helicopters at high altitude. But if you put them in a giant pressurized bubble at high altitude it wont matter.

MikeB · Jul 8, 2024

My 20 year old Robinair is 1.5 cfm, and it works just fine for casual automotive use. It doesn't take more than 20 minutes or so to pull close to the -30" hg mark on my gauge. I see where Robinair suggests 1.5-3.0 cfm for automotive use. However, if you do automotive A/C for a living, you may want more than 3.0 cfm. Like someone said above, the cfm rating determines how long it takes to pull a vacuum, not how much vacuum a pump can pull.

Auto A/C vacuum pump. lots of CFM or Less CFM whats best?? A/C tech's please help.

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