A/C Lines disconnected overnight - Do I really need to Vacuum?

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66fyssh

66fyssh

Don't Stop Believin'
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Hey guys, I replaced the heater core in my 2008 Tundra and had the A/C lines disconnected overnight while the truck was parked in my garage this past winter.

It's getting hot in Georgia now and I'd like to recharge but I don't have a compressor. Will it hurt not to vacuum the system? Thanks!
 
Yup. It should be vacuumed down. Drive it down here and I'll vacuum it down and charge it for you.
 
RustyRatRod said:
Yup. It should be vacuumed down. Drive it down here and I'll vacuum it down and charge it for you.
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LOL, thanks for the offer!!

Dang, OK thanks! I'll start asking around. I haven't lived here too long but there's got to be someone with a compressor. I can buy a HF pump.
 
66fyssh said:
LOL, thanks for the offer!!

Dang, OK thanks! I'll start asking around. I haven't lived here too long but there's got to be someone with a compressor. I can buy a HF pump.
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That's the kinda vacuum pump I have. It sucks down with a compressor. I hate it because it;s loud as all hell, but it works good. lol Jones County ain't too far from Woodstock if you reconsider.

Still certified in AC, btw.
 
Thanks for the warning on the noise from the pump.

I was down your way Memorial Day weekend. We have our grandson staying with us (while his parents get their stuff together) and they live in Florida. We met them in the city of Perry on Friday to hand him off and picked him up on Monday.
 
Thanks, I'll find someone with a compressor and do it the right way, I hope to keep this truck another 10 years!
It's just been hot here the past couple of days and I'm ready for some air...
 
hey we did a vac'd down with the running car hooked up to a drop can in between the two cars . what better vac pump then a v8 , with a street grandma cam of course . pull 21 inches of vac . we bought a cheap vac pump , and though it away . never need one again .
 
What is a drop can?

Years ago, I had an aftermarket "knee knocker" on the 70RR. Once, I evacuated it, but putting a charge through it to "sweep" out most, then hooked it up to engine vacuum.

Any system that has been open and down to atmospheric should be evacuated.
 
RustyRatRod said:
Yup. It should be vacuumed down. Drive it down here and I'll vacuum it down and charge it for you.
Click to expand...
100% agreed Rusty. And don't just vac it down and un hook it and call it good. The last 20 min.or so removes the moisture that can make your ac not work well. I don't get in a hurry.
 
a drop can is in the middle of your lines from each car , this is to stop the running car thats vacuuming the other car from sucking the refreg'nt into it motor . tube from the car under vac as a drop tube down inside that drop can almost to the bottom of it . that cares the fluid into the can and puts it on the bottom of the drop can . and the vacuum line comes from the top of the drop can so no fluid transfers in to that running car , just vacuum . and this will draw it clean of all moisture and other crap . there was a write up in a gm service manual on how to do it . and we use duracool refrig 12a . its not r12 its cheaper and stays cooler then r134 as well . got it in this car , 50 deg coming out the exits at idle .

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wanna pull 18" of vacuum? just hook it to your manifold vacuum...Im kidding but I still dont know how that drop can works..where does the hose come from? I charged up a few open systems with R134 and they worked. Of course they had leaks in them so it wasnt a permanent thing. It got so bad I just started hooking up coleman propane to the low side via a torch head and an A/C charge hose. opened the torch valve and it sucked it right in there. Kept eye on gauge that was still on A/C hose and topper her off. Worked good enough until I scrapped it due to a leaking slipping trans. Too much to fix, not enough interest.
 
Lets' see.... south GA in summer weather..... lotsa sotrms moving through...... yeah, I'd expect the system has plenty of moisture in it after being open overnight.
 
HI,

You absolutely need to vacuum down the system. Any air in the system will cause very high compressor discharge pressures and possibly cause damage to system components. Also, 21 inches of vacuum is not really low enough, you want to get down to 29 or 30 inches. Those cheap air compressor driven vacuum pumps will not get down to that level. You need a real vacuum pump. You can often rent or borrow one along with an A/C gauge set from a local auto parts store. Also, if the system has been open for more than an hour or so I would replace the receiver/dryer or accumulator. The desiccant in those things soak up water vapor very quickly ( as they are meant to do) and are quickly ruined when open.

I would change the receiver/drier or accumulator and pull a good vacuum down to 29 or 30 inches and let the vacuum pump run at least and hour or two to pull out are much moisture as possible and charge new into that vacuum.
 
It's not just air which you want to get out of there. Probably more important is MOISTURE, because the moisture can and will freeze as it goes through the orifice / TXV and PLUGS the thing as it freezes. This causes interesting, aggravating intermittent problems.

Look at a chart of the boiling point of water. It's NOT 212F, you know, if it's NOT at "standard" atmospheric pressure

http://www.jbind.com/pdf/cross-reference-of-boiling-temps.pdf

At 20" Hg, the boiling point has dropped to about 160F.

But if you can get the vacuum down to 28---barely 29" Hg, the boiling point drops clear down to 75-80F

And if you can get it down to 29.8---on to 29.9" Hg, NOW the boiling point is down into the low 20F range and INTO BELOW ZERO!!!

What does this mean?? Simple. It means moisture in the system is going to boil off more easily and be carried off by the evacuation. So you can HELP this evacuation by doing these things........

1....Evacuate the system, if possible, on a warm day

2....If the car can be run, do so and get the engine up to temperature, and run the heater as well. This will get heat into the AC system, helping to boil off moisture.

Also, "in the day" before refrigerant recovery was "the law" it used to be common to run a "sweep charge" through the system, sometimes, more than once. How do you do this?

Think before you do something. Plan it.

Arrange to feed refrigerant INTO the high side fitting. This will "sweep" through the system just as if the compressor was driving it, fed by the pressure in the refrigerant container. This will push moisture and air out of the system.

To do this you need a way to VENT this. So you use a valve or second AC manifold so that as the low side comes out of a vacuum, and comes up "positive" in pressure, you OPEN the low side compressor fitting and allow the sweep charge to vent.

Of course "all of this is in the past," right? RIGHT!!!???
 
wish i could draw it for you , think of this . if you were taking fuel out of a can . would you do it by placing the hose at the top , not in the fluid ? no , you would put that draw hose down to the bottom , right . the drop can must be vacuum tight , but the process in reverse . the drawing vacuum running car is the top hose , not touching fluid . and the one from the car your drawing vacuum on , that hose goes to the bottom , and places the fluid in the can starting at the bottom . way away from the the vacuum draw side . and as far as the vacuum being low , it as not been an issue , to much fluid caused the system to not work properly . that was an easy fix . and with the duracool stuff we did not need as much coolant fluid . hope i drew a understandable picture , it does take a thousand words to paint a picture , lol !
 
Pete in NH said:
HI,

You absolutely need to vacuum down the system. Any air in the system will cause very high compressor discharge pressures and possibly cause damage to system components. Also, 21 inches of vacuum is not really low enough, you want to get down to 29 or 30 inches. Those cheap air compressor driven vacuum pumps will not get down to that level. You need a real vacuum pump. You can often rent or borrow one along with an A/C gauge set from a local auto parts store. Also, if the system has been open for more than an hour or so I would replace the receiver/dryer or accumulator. The desiccant in those things soak up water vapor very quickly ( as they are meant to do) and are quickly ruined when open.

I would change the receiver/drier or accumulator and pull a good vacuum down to 29 or 30 inches and let the vacuum pump run at least and hour or two to pull out are much moisture as possible and charge new into that vacuum.
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Hi Pete! Hope all is well up there in New Hampshire! The gauge regulator you helped me through is working like a charm. Its really nice to have a working gas gauge! Next on my list is a headlight relay kit...as soon as I save some moolah.

Thanks for the input. I'll look at replacing that receiver/dryer.
 
Just remember, if you run into a snag, I am here. Will be glad to help.
 
The only thing I've never understood about the whole vacuum down thing is; unless the entire system becomes a flat garden hose, how is 'all of the air' going to be removed? It ain't like 20" of vacuum is going to crush your metal hose so no air exists, or turns your compressor into a black hole..

The moisture, I get that. No air? Not sure about all that. Unless you work from the end of the system to the front and absolutely fill every void with refrigerant.. We all know how that works out..

I'm not trying to be a hater, I'm behind this procedure, I just think the proper reasoning should come to light.
 
People forget too that R134A has different properties than R12. The 134 needs the extra suction from a system vacuum more than the 12 did to help get it into the system. Also, you will never get all the air out. You can get more out with a charging and recycling machine, but never all of it.
 
you should have it done , by a pro air shop . if you think you can use garden hose for vacuuming lines . vacuum lines are very stiff walled hose , like the power brake can uses . sorry about responding . you must understand the basics of this job , well before going though with it , so sorry again .
 
Woods74 said:
The only thing I've never understood about the whole vacuum down thing is; unless the entire system becomes a flat garden hose, how is 'all of the air' going to be removed? It ain't like 20" of vacuum is going to crush your metal hose so no air exists, or turns your compressor into a black hole..

The moisture, I get that. No air? Not sure about all that. Unless you work from the end of the system to the front and absolutely fill every void with refrigerant.. We all know how that works out..

I'm not trying to be a hater, I'm behind this procedure, I just think the proper reasoning should come to light.
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Surely there must be some. But as with a lot of things, say, drinking water. All drinking water has "some" impurities. The trick is getting the impurities below an acceptable level. Same with an AC system. This in part is why I mentioned a "sweep" charge. We used to do this all the time. Depending on "what" we were doing.........pull a quick vacuum, check for leaks, introduce a quick "sweep" to push everything through the system, and then do a deep vacuum.
 
No air? Not sure about all that.
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Pressure, however slight, always moves high to low. A vacuum pump creates a low pressure "area" that any gas, or air, in the system will move towards that low pressure. Initially when there's 0 psi, or 14.7 psia, pounds per square inch absolute, the pumping rate or withdrawl of air is high. As it moves towards a vacuum, anything less than ambient pressure, the rate drops of course 'cause there's less to pump, but it does move out through the pump even if by molecule by molecule. Along with that, the moisture goes down, down, down. Pumps have a limit of how low they can go. A good pump can go to 25 microns or about 29.995 in.Hg vacuum. Most stationary a/c needs to see at least 500 microns of vacuum and HOLD for at least 5 minutes. Mobile a/c seems to live with a lesser standard given the equipment in most shops, and the use of hoses. Still, go at least below 29.98inHg and head pressures will be more normal. Moisture is the BIGGEST enemy of a/c or refrigeration. Refrigerant can break down to acidic compounds, and oils go sour, especially POE though PAG seems more resilient. Synthetic lubes are especially prone to moisture contamination, 100 times more than the older mineral oils. So dry is the key, and evacuation is the answer. One method to speed things up is sponging. Initially evacuate, then charge with dry Nitrogen to say about 20 psi. Then evacuate as low as you can go. Charge again with dry Nitrogen, and do a final evacuation. We call this a "triple evacuation" and can cut the evacuation drying time in half because the nitrogen is pulling the moisture out with it instead of waiting for it to come out molecule by molecule.
 
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greg r said:
then charge with dry Nitrogen to say about 20 psi. Then evacuate as low as you can go. Charge again with dry Nitrogen, and do a final evacuation. We call this a "triple evacuation" and can cut the evacuation drying time in half because the nitrogen is pulling the moisture out with it instead of waiting for it to come out molecule by molecule.
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"Pulling" is not the word I would use. The very reason we used to call it a "sweep" charge is that if done properly, you charge on the high side and the pressure of the sweep material PUSHES air, moisture, etc through the system, and as soon as the low side starts to "come up" you vent it, allowing the pressure from the "sweep" to do just that.......push most of it out.
 
You are close by and I have a pump and gauges, come on over we will get you fixed!
 
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