Vacuum for leak testing

[wptski]

Vacuum leak testing is almost meaningless. For comparison, I had a system holding 29in/Hg for over a month and I know it leaks under pressure. Most DIY in this forum don't have a nitrogen setup to pressure test which should be done first before pulling a vacuum. Not holding a vacuum will only find the larger leaks. An A/C system is a pressure system not a vacuum system.

[Dave in Texas]

Makes sense. Vacuum pulls in, while pressure pushes out. Maybe a tiny crack in a line would be re-mated under vacuum and pressure would reveal it?
Nitrogen readily available for the DIY'er and what is needed to introduce it into car system? Costly? Learning stuff.....

[wptski]

Makes sense. Vacuum pulls in, while pressure pushes out. Maybe a tiny crack in a line would be re-mated under vacuum and pressure would reveal it?
Nitrogen readily available for the DIY'er and what is needed to introduce it into car system? Costly? Learning stuff.....

I got my 40CF nitrogen/tank at a local Airgas and they are all over the place. Initial cost is a bit stiff but your buying the tank also but refills are not bad. A regulator about $50 or so. Call Airgas first about the exact cost and they probably sell a regulator to fit but might be higher than others.

EDIT:
I found my invoice, $129 for the 40CF tank and $23.52 for the N2 in March of 2014. I got this higher end N2 regulator: https://www.amazon.com/gp/product/B001D ... UTF8&psc=1

[mk378]

It only takes a couple oz of 134a to put 50 psi in a system for a basic static pressure test. You want to keep the pressure below the saturation point (i.e. no liquid R-134a in the system) so there will be an immediate pressure drop if there is a leak.

[wptski]

It only takes a couple oz of 134a to put 50 psi in a system for a basic static pressure test. You want to keep the pressure below the saturation point (i.e. no liquid R-134a in the system) so there will be an immediate pressure drop if there is a leak.

So you are saying that if a system can hold 50psi in it, there is no leak and it can hold, >150psi? I have a vehicle that held vacuum and 150psi for 24 hrs but still leaked from a new shaft seal. I read from a well known user here that new shaft seals can leak when new just takes 10 hours to break in. It never stopped leaking. I'll be putting another seal in it when I get to it.

[Dave in Texas]

Makes sense. Vacuum pulls in, while pressure pushes out. Maybe a tiny crack in a line would be re-mated under vacuum and pressure would reveal it?
Nitrogen readily available for the DIY'er and what is needed to introduce it into car system? Costly? Learning stuff.....

I got my 40CF nitrogen/tank at a local Airgas and they are all over the place. Initial cost is a bit stiff but your buying the tank also but refills are not bad. A regulator about $50 or so. Call Airgas first about the exact cost and they probably sell a regulator to fit but might be higher than others.

EDIT:
I found my invoice, $129 for the 40CF tank and $23.52 for the N2 in March of 2014. I got this higher end N2 regulator: https://www.amazon.com/gp/product/B001D ... UTF8&psc=1

Thanks for the information. Will look to learn more about this and procedures.

[72gmc4x4]

I need to buy myself a tank. I would have the other day, but the investment was more than I expected.

How long will 40cf last? As in rough number of times I can test an automotive AC.

I'm trying to determine if I should go with a bigger tank.

[wptski]

I need to buy myself a tank. I would have the other day, but the investment was more than I expected.

How long will 40cf last? As in rough number of times I can test an automotive AC.

I'm trying to determine if I should go with a bigger tank.

That I don't know! They start out at over 2000psi and I think that I'm down to maybe 1300psi. On the leaker vehicle mentioned above I've taken it to 150psi two or three times. I've also pulled a vacuum and just broke the vacuum with N2 and pulled it down again. A few times on a R410A dehumidifier taken to 250psi IIRC and broke the vacuum as well. Last use was to pressure test the brake lines I'm currently replacing(a real PITA) on the leaker vehicle taken to 900psi using a larger regulator.

The bigger you go, one must remember that you may need to move it around. I have this to move my 40CF from my basement to my garage: https://www.amazon.com/gp/product/B0062 ... merReviews but there are cheaper ones with plastic wheels.

[72gmc4x4]

I bought one. 60cf. Now I need to buy a regulator. I thought I had one but its different.

[wptski]

I bought one. 60cf. Now I need to buy a regulator. I thought I had one but its different.

What did that set you back and where'd you get it from?