Thom1

Hi Sharks:

Is this $14 a/c vacuum pump too good/cheap to be true???
<a href="http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=3952" target="_blank">http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=3952</a>
Can I use this pump to remove moisture, and preserve refrigerant volume in the car? I have one of the most powerful household 110 volt compressors: 15 gallon, 4.5HP, 11.9CFM, Porter Cable, as a compressor source. Are there better reasonably priced alternative vacuum pumps?

Is there a pretty simple guide to R-134A flush and fill?

Can I just use a cheap manifold gage set from the local parts store to service it myself?

Ps. This is not for the Shark. I have an old station wagon that I use as a truck.
<img border="0" alt="[jumper]" title="" src="graemlins/jumper.gif" /> <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" /> <img border="0" alt="[jumper]" title="" src="graemlins/jumper.gif" />

dr bob

Consider that the more air there is in the system, the worse the system will perform. I was working on a car the other day, where a schraeder valve was leaking some under suction. When I disconnected the pump, it took less than a second, leaking through a schraeder valve, to add 10 lbs to the system pressure. That costs about 15 degrees at the evaporator, assuming that there are no other effects like poor transfer and no expansion at the expansion valve. So just how much vacuum is this device going to give you?

To get all the moisture out of the system, you need to consider leaving the vacuum pump on and running overnight, especially if the ambient is less that HOT. Sucking the water out means you have to get the pressure low enough to boil it, and that boiling cools the remaining water down and slows the boiling process. Outside air continues to heat the moisture in there, the more heat the better, until all the woter is vaporized and sucked out through the pump. Lower pressure in there means more water will get carried out.

So, try the little venturi pump and let us know what pressure you see on the low-pressure gauge. The closer you can get to 30" the better you will be. That gauge set from the parts store will do fine, by the way. Use the red high-side hose to attach to the vacuum pump, the yellow hose to the R-134a bottle (do NOT try to use those little cans...) and the blue hose to the low-side port on the car. Once you have evacuated the car and the line to the bottle, with both manifold valves open, close the high-side valve (to the pump) and add some freon to get a little positive pressure. Move the red hose from the pump to the hi-side port on the car to watch that high side pressure, but that valve stays closed for the rest of the session. Charge by weight the rest of the way.

I found a laboratory-grade pump at an industrial auction for less than $100. Pulls down to a few microns, more than adequate for AC service. I also have a couple of ejector-style pumps, somewhat like the one you are considering. 24" of vacuum is all I ever saw from them, but admittedly they came from service on a packaging machine that didn't need more than that.

Thom1

Hi Dr. Bob,

Thanks for the analysis. I called their technical support, and the guy said it only works on R-12. He did not know why. He did not sale hoses and fittings.

Why in the world would this only work for R-12? Seems like the principals would be the same.

The pump hooks up to the high pressure side, OK. Then I could just run it for a couple of minutes (with the household compressor hooked to the hidden connection point not shown on the pump)?
<img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" /> <img border="0" alt="[jumper]" title="" src="graemlins/jumper.gif" /> <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" />

dr bob

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Thom:
<strong>Hi Dr. Bob,

Thanks for the analysis. I called their technical support, and the guy said it only works on R-12. He did not know why. He did not sale hoses and fittings.

Why in the world would this only work for R-12? Seems like the principals would be the same.

The pump hooks up to the high pressure side, OK. Then I could just run it for a couple of minutes (with the household compressor hooked to the hidden connection point not shown on the pump)?
<img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" /> <img border="0" alt="[jumper]" title="" src="graemlins/jumper.gif" /> <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Don't have a clue why they would say OK for R-12 but not R-134a, except maybe they have an out if you use it. Most folks who buy cheap puimps are too cheap to buy R-12, I'm guessing. Otherwise the vacuum isn't too particular to what follows it into the system.

When ou hook the pump to the car, the reason for going to the hih side is so you can suck all the air out of the hoses all the way to the gas bottle. Every little bit of air in there is destined to keep your AC from cooling well. That leads to the part about how long you leave the pump on there. AC shops might do it for 45 mins, OK if you have installed all new parts in a system that was flushed, with a new drier. Otherwise, you want to leave the pump on overnight to make sure that you have as much moisture removed as possible. Moisture mixes with some of the gasses to form an acid that will eat the aluminum prats where it comes to settle. These would be your evaporator and maybe the condenser if you don't use the system a lot. Otherwise moisture will freeze in the expansion valve, preventing it from cooling effectively until the ice goes away.

It all comes down to how much air and moisture is in the car and how badly you want to get it out. A little of either is a big no-no as far as system efficiency goes, so the better the pump and the longer you can leve it on the car, the better the chance you have of a cold system.

<img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" />

T_MaX

I vote NO!

The use of the word pump is well, used very loss here.

I have used a device like this to give me quick vacuum off of an air line (air solenoid operated) to pick up small plastic parts out of a mold.

They are not really designed for A/C work. It will take at least a 10 hp 100 gal. air-compressor to keep up with the air demand that "pump" requires for long term use.

Good luck, if you were closer I could lend you one like it so you could see for yourself without putting out the duckies.

V-Fib

The pump you got from Harbor Freight, has a threaded fitting that R-12 used. Of course the R-34 uses a different thread fitting. You can get the adaptor fitting from an auto parts store (mine came from O'Reilly) but it will probably have to be ordered. I got mine in 24 hrs. This also keeps you from using R-12 Gauge/Manifolds on the R-34 systems.

Anthony Tate
79/928 Silver Metallic

V-Fib

BTW, Max is right, I ended up buying an electric pump to do the job properly
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
Anthony Tate
79/928 Silver metaliic

Bill 86.5 928s

Reading this thread has peaked my curiousity. Is it possible to evacuate or purge the A/C system first with nitrogen to remove moisture? Could you then pull a vacuum for 45 minutes or so? Does nitrogen create a new problem or acids?
I will be recharging my system soon as it does not work. The condenser was replaced and leaks are yet to be located, I bought the 928 with the air not working....Thanks
Bill

T_MaX

I have never used nitrogen, but I have used CO2.

It is still recommended to vacuum it out and than checking for leaks prior to filling.

There is no short cuts on this one guys

dr bob

Hmmm...

Adding nitrogen doesn't purge water out. N2 sits on top of a puddle of water in there just as good as air or freon does.

Nitrogen is functionally non-condensible at the temps and presures you see in your system. You still need to evacuate all of it to get decent system performance.

As much as I believe in DIY projects, there are some like this that probably deserve pro attention. They already have the tools and equipment to evacuate, charge, and leak-check the system for less than the cost of buying a good vacuum pump yourself.

I know that there are write-ups on some tips pages that brag up results of recharges with no pump at all, using an old AC compressor as a vacuum pump, etc. I also know that you can never get your system as cold with any air in it as you can a system that's been properly evacuated of air before charging. Maybe if you did a dozen or two fill-and-purge cycles you could get the freon purity somewhere close to what you'd see after a proper charge. That would mean using almost 40 lbs of gas for a dozen cycles of purging, so you get the idea.

For all the time spent for a once-in-a-blue-moon activity (you are going to fix all the leaks, right?) you can pretty easily justify the right tool or profesional support.

With all the interest, maybe some of the regional OC groups should consider an investment in a few of these infrequent-use tools. SoCal group has access to this stuff now. ;-)

Dozman

Thom,

I would say do not wasting your $$$, the manufacturer does not state or claim that the vac will vac down to at least 500 micron. At 500 micron you have removed the water moisture that is in the system. If you do not remove as much moisture in the system as you can, you are asking for headaches later that will cost more $$$.