A/C Evacutaion ?

[brcorp]

I'm in the process of resurrecting my A/C. I'm trying to verify the system is leak free prior to charging it. I evacuated the system to 24 in-Hg (it took about 3 minutes) and left the pump on for 10 minutes. After three hours there was no change, still at 24 in-Hg. After 18 hours it had dropped ti 20 in-Hg. Is this a problem?

[Jim Sims]

Yes, you have a leak. What type of pump are you using? Given Tuscon's alitude (2600ft?) I would think you should be able to achieve 26 inches or better. Dropping to 20 inches means you definitely have a leak. Jim

[brcorp]

Tucson's altitude is about 2400 ft.

So after 18 hours you'd expect the level to still be at 24 in-Hg. What about the effect of temperature. I evacuated the system at about 3:00 pm on Saturday (temp about 85 deg F) and and reread about 16 hours later 7:00 am Sunday (temp about 40 deg F)

[scottb]

The system should hold pressure, or vacuum. If it does not, then you have a leak. Do you have barrier hoses? If not, then that's the place to start.

Don't waste the time (or money) recharging until you track down the source of the problem.

Scott

[BGCarrera32]

The place to start is o-rings and checking fitting crimps...don't throw money at barrier hoses until the easy stuff is ruled out.

-BG

[scottb]

Originally posted by BGCarrera32
The place to start is o-rings and checking fitting crimps...don't throw money at barrier hoses until the easy stuff is ruled out.

Good point! If you're using R12, however, you'll want barrier hoses. If you're using R134, you can periodically top-off the system on a DIY basis.

[BGCarrera32]

Originally posted by scottb
Good point! If you're using R12, however, you'll want barrier hoses. If you're using R134, you can periodically top-off the system on a DIY basis.

Ah no...other way around. R12 was the original factory gas...

[scottb]

Originally posted by BGCarrera32
Ah no...other way around. R12 was the original factory gas...

No, I was correct. The factory hoses were designed to leak. That's why the a/c systems don't hold a charge for more than a season or two. (I've heard that the molecular structure of R134 is smaller than that of R12, and that it leaks through non-barrier hoses faster than R12). With the skyrocketing cost of R12, you want barrier hoses to retain the R12 within the system, with no leaks. If you're going with R134, you can retain the original, non-barrier, hoses for two reasons. First, R134 will not harm the ozone like R12. Second, you can buy R134 at your local Autozone and top-off your system on a DIY basis. Thus, leaks are an annoyance, but nothing more. R12 requires an (easily obtained) EPA license.

[brcorp]

Originally posted by scottb
R12 requires an (easily obtained) EPA license.

How do you go about getting an EPA License?

[ruf-porsche]

Originally posted by brcorp
How do you go about getting an EPA License?

You can take a test on-line.

Go to the EPA website and lookup license or certification.

[mtburman]

or.......since your in Tucson, R12 is available in Rocky Point, $8/lb, in 2 kg cans, but of course, your not supposed to bring it across the border.

really try to understand your a/c system before working on it, more is not always better and there is some risk of injury.

[Thack]

I think losing 4 in of vacuum in 18 hours may be a loss due to the hoses on the test equipment. Most shops only test for vacuum for a few (no more than 3 hours) Test again for three hours. If it leaks down in three hours, get some soapy water put it on the connections to the compressor and any other fittings you may have disturbed.
I converted to R134 without much of a problem. Email for details.


Mike

[cmonref]

Soapy water on a fitting works only with pressure in the system to blow bubbles. With the system under a vacuum, a leaky fitting might draw the soap into your system -- not a desirable result.

[Thack]

I'm so sorry. You're right. I had such a large leak that I pressured the system with plain air. You can change the fittings to R-134 if you have a small leak and use R-134 to detect a leak.

[Rondinone]

I'm going to diverge from the rest and say that you may not have a leak. If there was significant moisture in your AC, like if it sat open to the air or was just empty for several years, there may have been considerable moisture. The evaporation of water under vacuum is a thermodynamically governed process and can take a while. i.e., your vacuum started out high but decreased slowly as liquid or adsorbed water became water vapor inside your hoses. Whenever I work on an automotive AC, I leave the pump on for at least an hour. Did you change your receiver/dryer before you pumped it?

What kind of pump are you using?

[brcorp]

Originally posted by scottb
No, If you're going with R134, you can retain the original, non-barrier, hoses for two reasons. First, R134 will not harm the ozone like R12. Second, you can buy R134 at your local Autozone and top-off your system on a DIY basis. Thus, leaks are an annoyance, but nothing more. R12 requires an (easily obtained) EPA license.

Assuming my system has no leaks, how long before the R-134 leaks out with the stock non-barrier hoses?

[ruf-porsche]

Originally posted by Thack
I'm so sorry. You're right. I had such a large leak that I pressured the system with plain air. You can change the fittings to R-134 if you have a small leak and use R-134 to detect a leak.

Pressurizing a system will cause moisture in the air to enter the system. That is why a system must be evacuated prior to installing the new refrigerant.

Evacuating the system lowers the boiling point of water which cause it to turn into a gas state and allows it to be removed from the system.

Never pressurize a system to look for leaks. Recharge with a small amount of refrigerant and use either an electronic snooper or add dye to the system to check with a black light.

Regards

[jdowty3]

Like Rondinone asked, did you replce your receiver/dryer? An almost 20 year old receiver/dryer is probably no good and will impede the efficientcy of your system. Also, did you replace the expansion valve? They are fairly cheap ( $25 from Hancock Industries ) and better to place it now than later and have to do the evac/recharge again.