I have an 07 uplander with front AC
The AC system has been open for about 3 yrs. last year I filled it with refrigerant and the compressor worked. I had cold air for a day before it leaked. last year in order to find the leak i put regular shop air into the system then used soap&water: i found condenser holes...
a few days ago i got the new condenser and drier in. i tried to pull a vacuum on the system but i could only get 26-27 inches of mercury after 1.5 hrs... its a new pump, new gauges. the gauges showed 29.xx inches of mercury on the pump by themselves. when removed from the pump, the AC system loses 6-7 inches of mercury in 5-10 minutes off the pump but stabilizes at about 16 inches of mercury and holds it there all night long...
i am in the flat midwest, it has been 80-85 degrees Fahrenheit on the days I checked vacuum. the gauges and vacuum pump are new by OEM TOOLS from autozone. the gauges are zeroed properly. the pump exhausts vapor that smells just like my AC system...

is only 27 inches of mercury during vacuuming acceptable on an old vehicle? the AC system is losing 6-7 inches of mercury in 5-10 minutes with the pump off, but then it stabilizes at about 16 inches of mercury and holds it there all night long ... is this acceptable enough to start putting refrigerant in? should i keep vacuuming? it probably isnt worth it to chase more leaks... everything is buried... but i will put in dye anyways. just curious to know how long do you ac experts suppose she will keep refrigerant if i fill her now??
many thanks in advance

 

probably has more leaks. vacuum again and charge the system and see what happens.

 

update:
i believe the system was very wet. i know pag is very hygroscopic and i know the system was open for a longtime. i heard that most of the pag is on the high side (cant confirm that) and i did find that pulling vac through the high side only seemed to pull a deeper vac to 28-29. i also warmed up the motor a few times which surely increased temps and helped it boil off. and i also pulled the high side only after countless hours of pulling low side only and both sides together so it may have just been that it needed many hours of time on the little vac... who knows.

i heard that if you warm the vehicle up and pull high side only that you can pull pag oil out of the system, which i wanted to do but cant confirm actually occurred... either way the pump exhaust had smoke/vapor after 12+ hours and it looked like it could have went for 12 more but i was done messing with it

i checked vacuum decay and it held at 28-29 inches for 30 mins so i refilled it with a can of refrigerant with 'additives' like boosters and sealers and lubricants and water/acid eliminators. that was all in the same can. i am not sure if the 'additives' should count toward the refrigerant capacity or the pag oil capacity... i have not found a definitive answer there.

i filled it faster than i wanted to. likely overfilled it if the 'additives' count toward the refrigerant capacity instead of pag capacity...
it was 95F yesterday and it was probably in the 60s every other time i have messed with refrigerant... plus i think all the other systems were open to atmosphere vs this one which was vacuumed down and holding the vacuum... either way, the speed at which it sucked the can in was significantly faster this go round and caught me a bit off guard

cooling was better than nothing but not good. dash air went from 120F to 68F. i couldnt get it lower than 68F, but didnt try either. low pressure seemed too high at 50 psi, high pressure seemed low at 175psi for what was then 85F ambient temps. under some driveway revving the psi's were 40 low, 200 high. it may just need a drive to settle out but i noticed the tranny line developed a leak at the radiator fitting so it is gonna have to wait. it may have too much refrigerant and additives... we shall see.

ultimately i am halfway happy with 68F in the vents on a 95F day where i know those temps were at 120F+ in the vents before... oh and the coolant temp gauge didnt even come close to moving past dead center with the ac/radiator fans running... which was great considering the van runs between 220-225F when the ac is out...

 

Under normal conditions, meaning the system is properly sealed, and the pump and gauge set are working correctly, vacuum should pull to 30” of vacuum within the first minute and hold while the pump is running. If the system doesn’t pull down to 30” of vacuum at all while the pump is running, there’s a significant leak preventing it from doing so, or there’s a problem with the pump.

For leak testing, vacuum at least 10 minutes, then monitor the vacuum for 5 minutes - it shouldn’t lose more than 2” vacuum. If it does, there’s a leak. Make sure to close the valves on the gauge side of your set otherwise you could be getting a false result due to leaks in the gauge set of the vacuum pump - it doesn’t matter how new they are.

Those pressures are not adequate and it’s probably due to the system not being vacuumed or charged properly. For it to have been exposed to atmosphere as long as it was, the compressor may not be working properly or the expansion valve (if equipped) could be sticking.

If you put dye in it, tracing the leak shouldn’t be too difficult.

 

Sorry, you added the A/C sealer, but I know that you are frustrated and simply want this issue to go away. Were I you, i'd put a new accumulator and a rebuilt pump, as you did, but install new o-rings and use R-134A with a leak detector. If it will hold at -27 PSI, that should work, but losing vacuum that fast means there is indeed a leak somewhere.

 

yeah, i did some digging and discovered that at about 1000ft above sea level that the highest achievable vacuum is slightly higher than 29 inches of mercury. we are about 850 feet above sea level here.... the other thing i learned is that the moisture from an long open system will attach to the pag oil and off gas when you try to pull a vacuum. apparently this will prevent you from pulling a deep vac and mess with the vac decay test... the fix for this is apparently to get rid of as much old pag as possible and shoot nitrogen into the system then vac it out. do the nitrogen charge/purge 3X. then vac it down like normal. OR just vac it down for many hours, and run the motor to create more heat and burn moisture/oil off faster since a little heat goes a long way in a vacuum... this combined with pulling the vac on the high side only helped me achieve a good vacuum and pass a 30 min vac decay test after 12+ hrs on the vac pump.
i am confident that the system is sealed. i believe last time i charged it i needed to follow a procedure before it got really cold at the vents. it involved going like 35-50mph for a handful of miles or mins to normalize the system or something... i remember driving it on an old state route when i did it... i will have to find the procedure, but it got a lot colder after that drive i remember.

 

i read that a very wet system will mimic a leak in a vacuum decay test and also prevent a deep vac til it is out of the system.
i finally got my vac down to 28-29 inches of mercury on the system after running the engine, which significantly increased pump exhaust. it held that 28-29 vac for 30 mins so i ran with that

 

There’s literally no point in only vacuuming the high side of the system - the entire system is connected via the compressor and expansion valve or orifice tube. Only vacuuming one side of the system just means it’s going to take longer to get a proper vacuum in the first place.

 

i agree that they are connected, but the guy said theres more pag sitting on the high side than there is on the low so it would be faster/better to pull from the high side if i wanted to target the moisture in the pag and maybe even the pag itself... 1000 ways to skin a cat. i already skinned it anyways.
really my only question at this point is whether the 'additives' count towards the pag capacity or the refrigerant capacity or they dont count at all?... cant get a clear answer there... the can says the additives are lubricants, boosters, acid/moisture eliminators, sealers.

 

Virtually no manufacturer recommends any "additives" so you are not going to see a spec for it. But if it is a 12 oz can of refrigerant with "whatever" than you have 12 ounces of refrigerant.

Going back to your initial concerns - every time i've had a system not pull to full vacuum within a few minutes, it's been an obvious leak either in the gauges/vacuum pump to service fitting setup, or something like a slipped o-ring at a connection. Full vacuum is close to 30" as possible, which you can't achieve unless you're in space. On a basic set of A/C gauges that will look like 28 or 29, doesn't matter beyond that they are not that accurate.

30 minutes of vacuuming a system is the rule of thumb to boil out any residual moisture. And you said you replaced the drier so that will do it's job as well. I think you've covered those bases just fine and then some, as long as you got the vacuum to hold.