A/C - electric vacuum pump purchase

If you're handy with a soldering iron, just buy a cheap used refrigrerator and remove its compressor. Solder a refrigerant fitting ont he suction line, and presto- vacuum pump for $20 or thereabout.

Just remember to feed it a teaspoon or two of refrigerant oil (use the mineral type for R-12 or R-22)into the suction line with it running every few hours of use.

I'll second that motion. I used those for several decades--actually one is still in use that I made in the 70's--and they do a nice, quiet job. You may first want to do a little research to determine one that will be faster than others. If you wish it to look more 'presentable', you might make a small hand-truck to fit it & roll it around on. I did that and did the same thing on my 120-amp battery charger made from a washing machine motor and an alternator-with-regulator. Both were small, compact, portable, and self-supporting around the cars. s

Fittings can be change to what ever you need as long as you have the right hose connect to the system. Links below have some. Also the ACkits.com has a air cond repair forum that can help you on your questions and problems on AC repair. Good luck MT

Great ideas guys, but I was looking for tips when buying a vacuum pump. I have a $200 budget for the pump and do not need to play with refridgerators.

I need to know if I can buy a pump with some kind of oil filter, is it worth it to pay for dual stage one or not, etc...

I like the DIY solution with the refridgerator compressor, but there will be considerable work involved in looking up fittings, assembling it in some fixture, taking care of oil consumption or filtering the output/vent - this is discouraging enough... That is why I want to shell out some money and buy a real thing.

The links I posted has the pump with kits but look around on the web page they should have pumps seperate. And as said they can answer all questions you may have on the pumps. Good Luck MT

How the pump is influenced with a residue of the refridgerant left in the system before vacuuming it ? Will the switching the pump between R134 and R22 systems do any bad things to the vacuum pumps, its o-rings, seals, etc ?

Thanks. I can find many pumps - the point is to choose the right one. And this task is what I needed help with...

As said ackits.com has a good AC forum with the best AC people from all over the world. Run a post on it and they will be glad to help you.

Good Luck MT

It's not. This has been done for years without problems.

Thought you were doing automotive? Where does the R-22 come into the picture? Switching between refrigerants is not a problem. As long as you maintain the vacuum pump (basically oil changes) you'll be fine.

Robinaire, Mastercool, and Inficon all make very good vacuum pumps. Pick the highest CFM and the lowest micron rating that fits your budget. To service properly, you need to draw a deep vacuum, 500 microns is your target so, you want a vacuum pump that rated at least that good to begin with. I'd also budget for a micron gauge so you -actually- know that you've pulled a deep vacuum.

I will look for that manufacturers - so far I found really popular in stores (and cheap one - about $120+S&H): FJC 6908

stage, 70 microns, 2,5 CFM, 1/4 HP 120AC motor. Any personal experience with that pump in the group ? Is it something worth considering or is it a cheapo "made in china" ?

How microns translate to inches of mercury ?

I am not sure how to compare one pump rated at 28 inHg and one rated 70 microns... Which one is better and how much better ?

Is that 500 microns a requirement stated by the car manufacturer repair manual or something you come up based on your own experience ?

I was guessing the standard A/C pressure gauges will be good enough for the job... Good idea.

Sorry.. I thought you were just poor. I didn't realize you were poor and lazy.

Steve B.

Sorry, not familiar with that brand.

Atmospheric pressure equals (appx) 760,000 microns. if we divide 760,000 by 29.9, we get 25,418, so one inch of mercury equals 25,418 microns. To attempt to use a standard manifold gauge set vacuum gauge to assess vacuum is akin to trying to measure crankshaft main bearing clearance with a yard stick.

A pump rated at 28 in.hg. is basically worthless, a waste of time. A pump rated at 70 microns is probably a laboratory piece.

It's the standard for the AC industry.

For most people and most repair shops, it is.

My view; it's better to spend $250 on a vacuum pump plus $150 on a micron gauge and be certain that the moisture has been evacuated and there are no leaks versus spending $400 on a vacuum pump and wonder. You can pull XX.X vacuum where water will boil in the system, but it takes a much deeper vacuum to actually remove the moisture.

I know nothing about vac pumps BUT I see all kinds of them in pawn shops in the industrial side of town. Seems like every pawn shop has 5 or 6. Some with tanks meant for a/c work and some meant for ???.

???

What was that, Steve ?

Do you have some problem when people do not take your advice ?

I said I like you idea to make a "getto pump", but I stated at the begining that I can afford buying one from the store...

No need to play meanie, Steve! :-)

OK.

Cool. So microns are just 1/1000 of milimeters of mercury...

1/1000 of Torr. Or 1 umHg :-) Got it. Now it is simple :-)) Thanks.

But most of the car repair shops just use them on day to day basis.

70 microns is the rating of this $120 pump I found and listed above.

Cool. Thanks. Do they specify for how long time this

500 microns (1/2 mmHg) pressure should be applied to the system?

Can deeper vacuum be substituted with longer vacuuming time ? If water boils, it only takes time for it to fully evaporate.

Just buy one from a reputable brand name and forget all that. You don't need multi-stage pumps for evacuating AC systems. They don't have oil filters (or filters of any kind). The oil should be changed periodically in any of them, because vacuum pump oil becomes contaminated with moisture.

No. Unlike the compressor in an AC system, a vacuum pump doesn't depend on the refrigerant to CIRCULATE the oil. So it can use a mineral base oil that won't be damaged by any of the refrigerants normally used. The problem is that in a system where the refrigerant has to actually carry the oil, you have to use special oils that sometimes are sensitive to chlorine-containing refrigerants.

You got it!

Yes, and that is not a good thing. You gearing up to do your own work gives you the opportunity to take it up a notch.

Sounds good then.

There is no time standard for 500 microns, when you reach it, you have removed as much of the moisture as is needed. The micron gauge replaces vacuuming to a time standard. Vacuum to 500 microns, shut off vacuum pump, isolate, if the micron gauge holds below 750, you're good to go.

The only way to know is to check against a vacuum gauge of sufficient accuracy.

That's not necessarily true, and still doesn't address whether there is still anything leaking. The micron gauge covers that.

OK, but if a dual stage pump is cheaper than single stage ?

I was thinking of some kind of oil blockage on the outtake and some check valve on the intake to prevent loosing vacuum and contaminating target system with pup's oil when pump is turned off. But I guess this can be achived with closing a cut off valve before shuting off the pump, right ?

Get it. Thanks.

BTW - Is "Steve" the same person as "Steve B." ? Steve B. sounds like a real jerk, but Seve with no B is very helpful - thanks!

Most vacuum pumps have check valves as part of their design. There's usually an expansion chamber that traps oil droplets and allows them to return to the sump, not a filter.