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Blurvfocus

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Discussion starter · #1 ·
Has anybody ever used one of those venturi type vacuum pumps to evacuate their AC system?

How much air volume do you need to run it? Do they work OK?

Thanks for any info.
 
#3 ·
Blurvfocus said:
Has anybody ever used one of those venturi type vacuum pumps to evacuate their AC system?
Click to expand...
yes

How much air volume do you need to run it?
Click to expand...
alot


Do they work OK?
Click to expand...
just ok



I only ever work on AC maybe once ever 5 years or so.

For that they're fine.


I think they say 75 psi.... That's not enough. To pull max vacuum I need 95 psi at my regulator before the vacuum pump. (50ft of 3/8 hose after regulator)


My 30 yr 2HP compresser can't quite make the air volume at 95psi. Gets to about 85psi, then maxes out with a 100% duty cycle.

So I needed to figure out when the compressor turns off. (118psi)

I'll turn the AC gauge set off. turn the air pressure down at the compressor and let the tank pressure built to 115psi, then turn the air pressure all the way up. Then open the valve at the gauge set again.

The tank air slowly bleeds down as the compressor can't keep it at 115psi. But I get about 5 minutes of 95psi output to the venturi pump. When it starts to drop below 95psi, gauge valve goes off and repeat above procedure.



If you have a big air compressor, you'll be fine, just adjust air pressure for max vacuum. (have the valves closed on the end of the gauge set hoses so you're only pulling a vacuum in the gauge set and gauge hoses)


If it matters, my vacuum pump is a 30yr robinair......
 
#4 ·
That sounds like you're putting pressurized air in [scratch]

Sorry Blurv, I have no idea what you're talking about. This is what I use- not the same brand- I'm not sure what you mean by venturi vacuum pump. Can you give a pic? This one is also what residential and commercial AC techs use to vacuum their systems as well. You should be able to rent it from a parts store- but check it before they give it to you to see if the oil is properly filled. Improper oil level doesn't hold a vacuum.

Image
 
#6 ·
He is putting compressed air "though" it. exactly the same principal as a carburetor or a paint sprayer (not a gravity paint sprayer).



whynotthinkwhynot said:
That sounds like you're putting pressurized air in [scratch]

Sorry Blurv, I have no idea what you're talking about. This is what I use- not the same brand- I'm not sure what you mean by venturi vacuum pump. Can you give a pic? This one is also what residential and commercial AC techs use to vacuum their systems as well. You should be able to rent it from a parts store- but check it before they give it to you to see if the oil is properly filled. Improper oil level doesn't hold a vacuum.
Click to expand...
 
#8 ·
Blurvfocus said:
Thanks everyone.

I have a 3.5 horse compressor. 20 gal tank. It knocks off at 105, but I can adjust it up a little I guess. Is this big enough?
Click to expand...

Should be enough. Run as short of a hose as possible from compressor to venturi pump.


Your compressor might be big enough that it will hit the 105 and shut down even with the venturi pump hooked up.


Then the venturi pump will lose vacuum as the pressure creeps down to the cut-in pressure...........


You might have to add a small leak so that the compressor tops out at 103-104 and you're running continously.
 
#9 ·
There, now I know why they call it a venturi vacuum pump. It doesn't really matter as long as you get around -30 "hg. You might even get more with that one- have you hooked it up through gauges to see what you get?
 
Discussion starter · #10 ·
whynot- No- I'm just trying to decide if I should bother to buy one.

emsvitil- I understand what you're saying-
Maybe I'll give it a try. I'll submit a full report later.

Thanks-
 
#11 ·
It'll work "ok". But only ok. If you are done repairing the leaks in the system and evacuating it for a fresh charge you really should bake the system (pull a vacuum) on it for about 45 minutes to boil all moisture out of it at about 30 inches of mercury. Its going to be taxing on that compressor at any rate running for that long. The downside with this system is that you can't monitor the vacuum after it is done pulling it to make sure it doesn't leak vacuum. If it leaks vacuum it will leak under pressure and you have another leak to take care of.

It'll work, but be prepared to probably fix something in a year or so again. Its best to take it to a shop where they have the correct equipment.
 
#12 ·
I happen to be working on my sisters Saturn AC at the moment, so here's an observation.

Since I don't want to run my compressor continously for 45 minutes, I tend to run 5-10 minutes, close the gauge valves,let the compressor cool, then run it some more.


Air is trapped in the system. (I'd guess in the compressor).

I'll pull it down to 30 inches, then let it set for awhile.

Come back and it's at 25 inches. Pull it back down to 30 inches, let set.....

Now it's at 28 inches.......

After about 45-60 minutes total time at 30" it will stay at 30"


So you need the 45-60 minutes at 30 inches not just for the water vapor, but to make sure you've pulled out all the air from the nooks and crannies............
 
#13 ·
I disagree, that looks like a hose fitting to me on the pump pictured, so you should be able to hook the yellow hose into it then use the valve on the low side hose to trap vacuum. That's basically the same thing if you use an electric vacuum pump. Before you cut the pump off, you close the valve on the low side hose, remove the center hose from the pump and secure it to the manifold, then open the low side up again. Typically I lose about 5 "hg. I take a new reading, and wait 30 mins or so to be sure the system is sealed.
 
#14 ·
When I'm ready to put in the R134a, I'll hook up the can and tap to the yellow hose.

Leaving the tap closed, hook up your vacuum pump to the high side hose, open the high side valve and suck out the air in the gauge set and the yellow hose.

Close high side valve, turn off vacuum pump and you're ready to release the R134a into the system............
 
Discussion starter · #15 ·
jetrinka said:
Its best to take it to a shop where they have the correct equipment.
Click to expand...
I like to buy what I need as I need it. This is how I got all my tools. I'd much rather pay as much or even a little more for tools to do the job than farm it out, because then I have the equipment forever and it's fun to monkey around with all this stuff. That's how I got my alignment rack! OK I don't really have an alignment rack here but I would if it weren't for Marybeth.
 
#16 ·
Posted via FF Mobile Hear the Marybeth..... (grin) If it`s affordable for you, the electric powered vacuum pump would probably be the best bet for ease of use & adequate performance, overtaxing a compressor could be more pricey in the end.... (electricity, repairs...)
 
Discussion starter · #17 ·
^^yeah, after all is said and done, I guess I'll get a real pump and get it over with. I'll have to hope that all the air conditioners go on the fritz so I can justify owning it!
 
#18 ·
Eh, I just fixed my friends and charged them to pay myself back for getting mine. Mine is due for an oil change now. I would like someone to make one of these with a freaking carrying case. Mine has a handle, but I use residential electrical wire wrapped around the box to tote it around.
 
Discussion starter · #19 ·
I haven't had to work on an air conditioner in a couple of years. And the old Fred Flintstone r-12 systems, I'd just hook up one side and open both service valves and blow freon thru it. Seemed to work fine...
 
#20 ·
I was a can-adder back when R-12 was the thing to have. I didn't learn how to work on AC's until about 12 years ago or so, but I just add through the manifold also. I would not connect both lines at the same time though- especially not with a can on the manifold. R134 head pressures can reach 300 psi, and I doubt that little refrigerant can could handle that kind of pressure.

Some day I'll be either installing a 4.0 in the Aerostar, or replacing the 3.0 that's in there. Either way, I'm giving Duracool a try in there before I put it in the wife's van. I'm curious to see how the hydrocarbon refrigerants are better- if they are. The cost difference is between typical 134 and super duper synthetic cooling booster O-wow the best ever 134. Their oil is not that much more either, so I might get that as well although it isn't required.
 
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