DIY AC repair

[Paul]

FYI - DIY'ers need a vacuum pump to leak test and eliminate moisture from system once repairs are complete. They are usually expensive - here's an inexpensive option:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=924 75

[larryo340]

I agree those do work. I have one and found to work just like the expensive electrice motor vacuum pumps.

[MitchB]

You need a vacuum pump that can pull down to around 1000 microns or better to properly service an AC system. There are 760,000 microns in one atmosphere of pressure. The pump shown advertises it will pull down to 28.3 inches of mercury. This equates to roughly 25,000 microns. At this pressure, water boils at 78 degrees Fahrenheit. At this pressure, it would take a very long time to pull all the moisture out of a system that had been open. At 1000 microns, water boils at 1 degree Fahrenheit. Used as an inexpensive alternative, this pump will cause more problems long term.

Mitch

[69mach1]

Very interesting data.:bows: Does this mean a piston style pump does a better job?
I certainly need to learn more about A/C workings in a car to make sure i get it right:cool:

[larryo340]

You need a vacuum pump that can pull down to around 1000 microns or better to properly service an AC system. There are 760,000 microns in one atmosphere of pressure. The pump shown advertises it will pull down to 28.3 inches of mercury. This equates to roughly 25,000 microns. At this pressure, water boils at 78 degrees Fahrenheit. At this pressure, it would take a very long time to pull all the moisture out of a system that had been open. At 1000 microns, water boils at 1 degree Fahrenheit. Used as an inexpensive alternative, this pump will cause more problems long term.

Mitch
Technical data aside, I have used it on two cars with hose and seal replacements. The systems were only open for a very short time. It pulled system down to 28-30 inches of vacuum. Both cars were ice cold, one car i sold to a friend, and it's still ice cold (done close to 10 years ago)

[paheff]

Very interesting data.:bows: Does this mean a piston style pump does a better job?
I certainly need to learn more about A/C workings in a car to make sure i get it right:cool:

Actually, it's more like a rotary vane pump, and yes it does a better job. At 28 in/hg you likely will not dehydrate the system, which is the only reason, aside from removing non condensibles (air) you need a vacuum pump. Mitch B gave a very accurate description. If you get lucky and don't get moisture into the system, the $10 pump may suffice, however, you can't know. Dehydration is called for any time the system is open to the atmosphere, it's that ounce of prevention thing.

[JACook]

Technical data aside, I have used it on two cars with hose and seal replacements. The systems were only open for a very short time. It pulled system down to 28-30 inches of vacuum. Both cars were ice cold, one car i sold to a friend, and it's still ice cold (done close to 10 years ago)

See, here's the thing. To the uninitiated, there doesn't seem to be much difference between
28 in/Hg and 30. But in reality, the difference is huge. (Infinite, actually...)

This chart (http://www.robinair.com/acsolutions/acvacuum/chart12.gif) shows the boiling temperature of water at various levels of vacuum. Notice how much
difference only one inch of vacuum makes. The rest of the article here (http://www.robinair.com/acsolutions/acvacuum/acvacuum.php), explains in pretty good
detail why it matters.

At 28 in/Hg, water does not boil unless your ambient temperature is a bit north of 102F degrees.
Meaning, unless you live in Arizona, any vacuum pump that only pulls 28 in/Hg of vacuum, would
be basically worthless. The alleged vacuum pump that Harbor Freight sells isn't much better,
needing an ambient temperature of ~95F to relieve the system of any moisture. And that's IF
you're at sea level. You'll also need a good compressor that can supply sufficient airflow, and
won't mind running flat out for an hour.

In other words, it's a waste of money at any price.

I'm generally not a fan of venturi vacuum 'pumps', but if you've got your mind set on using one,
at least get one that works, such as this one (http://robinair.com/product-new/detail.php?id=1310&catid=11). Takes 4.2 SCFM of air at 75 PSI, and will pull a
29.7 in/hg vacuum (at sea level). At 7620 microns, that's still a far cry from the 50 microns that
even a lower-end real pump will pull, let alone the 20 microns a good one can pull. But if you've
got the compressor to run it, it'll work.

I'll stick with my 6 CFM Robinair...

[larryo340]

At that time I did have a high CFM compressor, again the systems I repaired were not left open for along time to outside air. Both cars that were done this way would blow so cold in hot & humid New York city that they could not be left on the coldest setting.

Science is great, but if my fat azz could get too cold, then I'm satisfied. ;)

[ckadiddle]

I have my own DIY a/c technique. I accidentally rammed the front end of the MM into the rear of an 04 Explorer with a trailer hitch. Some of the important a/c parts are replaced during the repairs due to the massive front end damage to my MM. The a/c now blows so freaking cold in humid 98F degree Florida summer weather that my face hurts. ;) There is always a silver birch lining to every dark cloud, I suppose.

[larryo340]

I have my own DIY a/c technique. I accidentally rammed the front end of the MM into the rear of an 04 Explorer with a trailer hitch. Some of the important a/c parts are replaced during the repairs due to the massive front end damage to my MM. The a/c now blows so freaking cold in humid 98F degree Florida summer weather that my face hurts. ;) There is always a silver birch lining to every dark cloud, I suppose.
That'll work
:beer:

[Stranger in the Black Sedan]

There is a $100 AC vac pump that Arctic Tools sells (They have Astro paint tools I have bought from them) that should do a much better job than that thing. I'm going to be picking one up shorttly because I have to vac down an AC system that has been open for a long, long time.