Automotive Air Conditioning Information Forum

I installed all new components for the AC system on my 73 corvette and pulled a vacuum on the system. After pulling 29" of vacuum I shut off the low and high side valves on the AC manifold gauge set and then shut off the vacuum pump. The system dropped down to just over 15" in about five minutes and after 30 minutes it was down to about 10" of vacuum. Is this acceptable or should I be looking for leaks in the sytem. I am a true novice when it comes to working on an automotive AC system and would appreciate any advise from someone more knowledgeable than myself. Thanks

As one who is working themselves out of the AC novice label...

That is not acceptable.

29" on a gauge isn't accurate enough. You want a Micron Gauge to properly gauge vacuum ($200) to 1st test the pump make sure it is providing adequate vacuum and then to test the system

Under 500 on the micron for the system overnight is good. a good set of isolation valves are important. Core replacement valves are nice ($75 each, 2 are nice)

Pressure test before vacuum test.

And then there's more stuff to consider but the above is a reply to your "is it good enough" question.

Gr8t73 wrote: ↑Mon Nov 13, 2023 1:23 pm I installed all new components for the AC system on my 73 corvette and pulled a vacuum on the system. After pulling 29" of vacuum I shut off the low and high side valves on the AC manifold gauge set and then shut off the vacuum pump. The system dropped down to just over 15" in about five minutes and after 30 minutes it was down to about 10" of vacuum. Is this acceptable or should I be looking for leaks in the system. I am a true novice when it comes to working on an automotive AC system and would appreciate any advise from someone more knowledgeable than myself. Thanks

Not nearly acceptable.

The leak could be in your AC system or in your equipment; check out the equipment first for leakage.

Cusser wrote: ↑Tue Nov 14, 2023 6:33 am

Gr8t73 wrote: ↑Mon Nov 13, 2023 1:23 pm I installed all new components for the AC system on my 73 corvette and pulled a vacuum on the system. After pulling 29" of vacuum I shut off the low and high side valves on the AC manifold gauge set and then shut off the vacuum pump. The system dropped down to just over 15" in about five minutes and after 30 minutes it was down to about 10" of vacuum. Is this acceptable or should I be looking for leaks in the system. I am a true novice when it comes to working on an automotive AC system and would appreciate any advise from someone more knowledgeable than myself. Thanks

Not nearly acceptable.

The leak could be in your AC system or in your equipment; check out the equipment first for leakage.

Good advice here. Micon gauges are nice but not mandatory. You must get it to hold a vacuum with whatever tools you use. Depending on you ability (equipment-wise). A leak test of the system is in order as well.

hi
in hg is

29.92 = 100 microns
29.9 = 500 microns
29.88 =1000 microns
29.82 = 2500 microns
29.53 = 10,000 microns

Many industrial/commercial compressors spec below 500 microns
Anything with a shaft seal 1000 microns
Above is with pump operating

Leak decay/ vacuum rise should be little as possible . A soldered system is a tighter system vs a system with rubber hoses o rings and shaft seals
The more leak proof a system is
1/ lower the rise
2/ the quicker the rise will plateau
3/ experience will tell u what is acceptable

The micron tool is great help . If u want the best get the best model u can afford . Wireless connection ,decay rate are just some of the better features .

Once u have used even a basic micron gauge u will never be without one , checks system and tools for leaks is great . Excellent for diagnosis .....