Trying to Pull Vacuum, only 22 Inces of Mercury

[marknhl]

Hello - I'm trying to fix the A/C on my 04 Saab 9-5. A buddy let me borrow his Pittsburgh gauges (Harbor Freight) and using a loaner vac pump from Autozone I can only pull 22 inches of mercury on the low side gauge.

I notice the below video, I should be able to reach 28 inches, whereas 30 inches is theoretically impossible. Again, I'm only hitting 22.
https://www.youtube.com/watch?v=lglPJuBXVeE&t=3s

Does this tell me that I have a leak somewhere since I can't pull a proper vacuum?

Other thoughts: Are the gauges just cheap junk? I replaced both valve cores and caps proactively. I have a receiver drier that I'm waiting to replace until I'm happy with the vacuum. When I close the valves, it maintains the 22 inches of mercury for multiple hours... however I noticed that even if I disconnect from the service ports, the vacuum stays. That doesn't seem right... as soon as I disconnect I would expect the vacuum to be broken. I checked around with a black light and saw dye around the expansion valve. I popped out the top hose and o-ring looks fine. The bottom hose I could not get disconnected and I was wondering if it was part of the valve but pictures online tell me otherwise. (If I need to pop that out, I'm not sure how I will be able to do that without breaking it off...) Dye was all over the expansion valve so I'm thinking this was a previous repair though I suppose it could be the issue.

I've had the car for 6 years and always had a/c issues but I've been able to fix it by just filling up one can of refrigerant each summer. This past summer, that no longer does the job so I'm trying to fix it properly. I've been watching videos and trying to learn. My brother in law is an HVAC tech but he doesn't do auto, so he's not sure how the systems different but he's thinking I still have a leak.

Any guidance is appreciated. Thanks in advance.

[bohica2xo]

When you connect everything up and switch on the vacuum pump, how long does it take to pull down to 22" hg?

Leaks are difficult to locate with a vacuum test. Generally we use dyes and sniffers with refrigerant pressure in the system to locate a leak

Once the leaks have been repaired you can use vacuum to check your work before charging.

[tbirdtbird]

You certainly do have a leak, and you have lost some oil along the way. Check for an oil/dirt stain along the lines and on the face of the condenser. The only way to tell if the evap has a leak is to put in a partial charge of 134 and then sniff the drain tube of the evap. Evaps leak commonly.

Check your gauges and your pump by connecting the vacuum pump only to the gauges and leave the red and blue port connectors of the hoses NOT connected to the car. You want to see if you can pull down the manifold gauge set to 29 all by itself. You are correct you can never pull to 30.
What kind of vac pump? Does it run on electricity or compressed air?
Also a loaner pump from Azone likely has never had the oil changed which will impair its ability to pull down properly, since it is heavily laden with moisture.
Post a pic of the couplers on the hoses.

[JohnHere]

I second the suggestion of changing the oil in the vacuum pump. It's a "loaner," so there's no telling how contaminated the old oil is. Use only vacuum pump oil that's specially formulated for vacuum pumps.

[marknhl]

When you connect everything up and switch on the vacuum pump, how long does it take to pull down to 22" hg?

Leaks are difficult to locate with a vacuum test. Generally we use dyes and sniffers with refrigerant pressure in the system to locate a leak

Once the leaks have been repaired you can use vacuum to check your work before charging.

Probably 5 minutes, so not long.

[marknhl]

You certainly do have a leak, and you have lost some oil along the way. Check for an oil/dirt stain along the lines and on the face of the condenser. The only way to tell if the evap has a leak is to put in a partial charge of 134 and then sniff the drain tube of the evap. Evaps leak commonly.

Check your gauges and your pump by connecting the vacuum pump only to the gauges and leave the red and blue port connectors of the hoses NOT connected to the car. You want to see if you can pull down the manifold gauge set to 29 all by itself. You are correct you can never pull to 30.
What kind of vac pump? Does it run on electricity or compressed air?
Also a loaner pump from Azone likely has never had the oil changed which will impair its ability to pull down properly, since it is heavily laden with moisture.
Post a pic of the couplers on the hoses.

I actually tried this earlier and the most I can pull is 22 even not connected to the car. I suppose this points to the gauges or the vac pump itself.

It's an electric pump OEM 1.8 CFM model: 57376 (VP115). Ideas on the vac pump oil? I could ask Autozone to provide me with some oil and change it.

[marknhl]

You certainly do have a leak, and you have lost some oil along the way. Check for an oil/dirt stain along the lines and on the face of the condenser. The only way to tell if the evap has a leak is to put in a partial charge of 134 and then sniff the drain tube of the evap. Evaps leak commonly.

Check your gauges and your pump by connecting the vacuum pump only to the gauges and leave the red and blue port connectors of the hoses NOT connected to the car. You want to see if you can pull down the manifold gauge set to 29 all by itself. You are correct you can never pull to 30.
What kind of vac pump? Does it run on electricity or compressed air?
Also a loaner pump from Azone likely has never had the oil changed which will impair its ability to pull down properly, since it is heavily laden with moisture.
Post a pic of the couplers on the hoses.

Pics didn't come through the first time...

2023 AC Troubleshooting Gauges photo_2023-07-25_01-12-45.jpg (164.17 KiB) Viewed 1554 times

[JohnHere]

I think the problem is the loaner vacuum pump. I suggest changing the oil first and then repeating the evacuation process. From one of the photos, it appears that the oil level is low anyway. This site's sponsor, ackits.com, carries the oil you need.

[bohica2xo]

Since you have no history with either item, I would try a different gauge set as well.

Perhaps the store that loaned you a vacuum pump has a gauge set you can borrow.

Usually a leak that won't pull below 22 inches is big enough to give a long evac time. Your system seems to pull right down.

[marknhl]

Great info - will try the oil and report back. Thanks!