I have a ’95 6.5TD Burb and I was wondering how involved this is? Do I need to vent the system first, and then recharge after swapping out the compressor? Can I replace the compressor without discharging the system? Anyone have experience doing this who give me some pointers?

Thanks,John Edited by: Juancho

It's easy to do but you must have the system evacuated 1st.

I just read some article that said you need to replace the dryer and Orifice tube also. Is that true?

this is necessary if you want to have a warranty on the compressor. if it does fail you have to prove that you at least bought a new drier and orifice tube when or near the time when you bought your compressor. if you take the front pass side turn signal light out it allows for access to the line that holds the orifice tube. they make a tool for removing the tube but it can be done with angled needle nose pliers. while the system is open you also should blow the lines out with compressed air.(per warranty specs.) when mine went out and locked up it filled the system with metal shavings from the compressor internals.

Thanks everyone for your input. Just one more question. How do I safely evacuate the system, and how can I tell if R-12 was use or some other refrigerant?

your 95 should be R134 but there should be a yellow sticker on top of the drier that has the type, capacity and oil requirements printed on it if not it should be the same as my '94 so if someone removed the sticker i can get this info for you off mine. to evac the system take off the cap on the low pressure tap(in the big line coming off the drier) and use a long handle philips screwdriver to press down on the valve inside(like a tire valve). the reason for the long handle tool is the refrigerant could give you instant frostbite if you used something shorter. there may be a very small amount of pressure left in the high pressure side, you can bleed it the same way or just be careful when you loosen the bolt that holds the lines to the back of the compressor thats how i've done it. Edited by: lupey6.5

The best way to tell if you have R12 or R134a is the fittings. R12 has threaded fittings and R134a uses the quick-release type. I believe your '95 uses an R4 compressor (R4 being the designation... it's also called the "pancake" compressor). My '97 uses the newer style, pretty sure it's a Sanden. Either way, it's not difficult. You'll probably have to switch to R134a if you don't have it already, so they'll need to put new fittings on. Make sure that you coat all the O-rings with Ester oil when you put everyting back together, and yes don't forget to replace the orifice tube and receiver-dryer otherwise you'll void the warranty on the compressor.

You'll want to have a shop evacuate the system, and then vacuum out all the air and charge it. Make sure that when they suck it down before recharging they let it suck for 30-45 minutes and then let it hold another 30 or so to make sure there're no leaks.

Good luck!

If you have R12 stay with R12. (This is only for capacity reasons) For economic reasons you can change to 134a, but you will not have the same cooling that you do with 12. Your truck is a 95, and is you already have 134a maybe from factory, so if that's the case, your married to that. Can't go backwards.


What did this thing do? Lockup on ya? It's best to determine what type of failure this thing had before throwing the new one on. Don't want to sentence the new one to death for failure of fixing original problem.


Please hide your identity if you are vent 134a now. EPA doesn't like 'dat now either. For some crazy reason this now "environmentally friendly" refrigerant is "supposed" to be reclaimed like all the others. Go figure.


It's a very GOOD idea to have the system put on a vacuum pump too. The longer the better. R134a has ester or PAG oil, and is very hydroscopic (holds water) Good vacuum is good for system. Have it monitored in microns when being pulled down to make sure no moisture is left in system.

Actually, the R134a is more harmful to the atmosphere than R12, DuPont just wanted their refrigerant to be the one everyone had to use. More money! So, buy out a couple politicians and, viola!

But that's another issue entirely, and not relevant to this forum. Make sure you know why your old compressor needs to be replaced (if it needs to be replaced), before throwing a new one in. Also, make sure they put dye in the system when they charge it so if it leaks out they can find it.

Thanks again Everyone,


I am confident that it is the compressor. It locked up on my wife during a road trip and burned right through the serpentine belt. She had no brakes or steering going 70mph and flank by 18-wheelers on either side. The mechanic that charged her $148 to change the belt, (you got a love those guys) had to disconnect the compressor all together.





So, just to recap, I really want to do this job by myself. I have worked on cars most my life, but I must admit, I have never changed out an A/C system. With that in mind, it sounds like I want to vent out the system. Remove the dryer, Orifice tube and compressor, than clean out the system with compressed air, and maybe some type of A/C cleaning solvent. Add PAG oil to the new compressor, coat any O-rings I use with PAG oil, install the new parts and recharge the system. Does that sound about right? Am I missing anything?


THanks,


John

The only need for the system to be properly evacuated is for envirnomental concerns about the R12/R134 escaping to the atmosphere. If you are of the mind that this is B.S. (as some think) you can simply loosen the hose connector on the back of the compressor and let the refrigerant escape, change the compressor and then charge the system with one of those kits you can buy at auto zone or advance auto parts for about $36.


This is not the "correct" way but is the cheapest, easiest fastest way.

I've changed out 3 compressors on mine, a 94 & 95. Blew a hose on one and the front seal on the other, other one was just making too much noise. As the refridgerent was already blown out on 2 of em it was no problem, the other one i just cracked the line and let her go, after all if you blow a hose or seal on the road thats where it goes anyways. The only thing i did different was to remove the grill completely, it gave all the room needed to do the work and change the orifice tube rather than poking around inside that light cover.


Once its back together you can drive without a re-charge providing your instructions say it was shipped with an oil that doesn't need to be drained out, the compressor won't kick in when the system is drained and the bearing is sealed and doesn't need refridgerent to run. I drove all winter before getting a re-charge on one of mine.

This is not the "correct" way but is the cheapest, easiest fastest way.





won't be the cheapest for long after you do it a couple of times

Bowtie,


Not sure what you are saying will happen but it goes without saying that doing it "right" most often yields a more predictable result but the cost/benefit ratio can be difficult depending on what you are talking about and what you need/expect from your repair.


I've haven't been burned on AC yet but yes, there have been other times I wished I had done things "right". It's a crapshoot based on an educated guess and the desired result.

Bowtie,


Not sure what you are saying will happen but it goes without saying that doing it "right" most often yields a more predictable result but the cost/benefit ratio can be difficult depending on what you are talking about and what you need/expect from your repair.


I've haven't been burned on AC yet but yes, there have been other times I wished I had done things "right". It's a crapshoot based on an educated guess and the desired result.





Your right on the crapshoot and most auto parts stores will void any warranty with out proof that other components were changed out also. The stores I worked at also wanted to see that you had flushed the system with an approved cleaner and that you bought the right oil. I also believe that puling a vaccuum on the system is another benefit offen overlooked. Just my .02 worth.


ROLL the dice

Of course what you say makes sense but the average guy can change the compressor and charge the system quite easily but very few backyard mechanics will have a vacuum pump.





Yep, roll the dice


You win some......you lose some.

Where exactly is the orifice tube? Is it located in the low-pressure tube connected to the dryer? Is it in one of the tubes coming off of the compressor? I realize it is by the Passenger side blinker but what tube is it located in. Also, what O-rings should I replace?

Bobt250,
I appreciate your frugal approach to the problem. In fact, before I posted here, changing out only the compressor is exactly what I was going to do. However, after reading every ones’ advice, I think I will just take my time and do it right. After the entire Orifice tub is only $5 and I think a new dryer is about $35. So, roughly $200 total for parts. That’s not too terribly expensive, and it is a lot better than the $1000 an A/C shop would charge me.

Yes, by all means change those parts. I was mostly saying that you could save the big bucks by avoiding the A/C shop and doing it yourself.

New 'O' rings usually come with a new or rebuilt compressor. Maybe this pic will help you out some. Best i could do for now. Take a peak inside your grill by the signal light, thats your condenser right in front of the radiator.


http://www.dieselplace.com/forum/uploads/A48_Untitled_0032_0001a.jpg

If you could find a friend, or someone with a vacuum pump, it would be a VERY good idea. Moisture is not friendly at all in the system, and vacuum helps to get out the moisture, non-condensables, and other junk out of the system.


Also, determine the cause of failure. If you have "black death," you may be in for some work ahead to make it right. There are forums out there dedicated to mobile a/c's, and their misgivings.


I talked recently to an automotive a/c engineer. He was telling me about the "black death" that occurs in these systems. He said that the high side gets to high and hot, that the oil actually cooks itself to the inside of the condensor, and pretty much ruins the heat transfer of the condensor, almost resulting in just about replacing everything. But read up on it yourself to get the whole story.

You want to swap both these parts anyway. If your compressor locked up it could have done so because of internal failure. if that is the case, metal shavings probably clogged up/shredded your orifice tube and probably shredded the dessicant bag (is that the right word?) inside the drier. No sense in putting a brand new compressor on, starting it, then having itself tear itself apart again due to metal shavings or parts that remained from an orifice tube.

I recently recharged my 95 with R12A. It Came from the factory with R134 and you cannot buy R134 in Canada unless you have a refridgerating ticket. R12A apparently is a hydrocarbon refridgerant. All I know is it worked very well for me.


www.duracool.com (http://www.duracool.com)

With regard to moisture,


I was once told that if you change the compressor without leaving the system "open" for any length of time you would be OK since moisture doesn't have time to creep in to the system. I've not had a problem doing it that way but I'm probably not the most experienced guy here and of course, doing it "right" is always best.

Thanks again everyone. I now feel very confident about dong this job, thanks to great input from all of you.





CanadianRigger,


That picture and explanation was extremely helpful.





Thanks,


John

Glad i could help! http://www.dieselplace.com/forum/smileys/Approve.gif

Be sure to use 2 wrench's when undoing the connection on the condensor where the orifice tube is or else you'll twist the tubing and have nothing but grief with the installing the new orifice. I would get the orifice from GM as the aftermarket ones i've gotten before needed some trimming to get installed and thats a pain!

I do refrigeration work for a living. My van had a compressor change out somewhere along the way. I put a vacuum pump on it, and the oil in the pump turned to milk real fast. That's an indiciator of moisture. I had to change out the oil three times before able to achieve a good vacuum, and low micron level on the gauge. I have no idea how in the world the moisture got there. I don't do automotive a/c work by trade. I don't know if the moisture actually entered throught the rubber hoses over time, or if it was a really bad compressor install.


If you change out the compressor quickly, yes, you limit the amount of air, moisture, non-condensables, etc getting in the system. We sometimes do that for a drier change on the fly after a system burnout in our trade. After you have the system pumped down, it will still "outgas" and provide a slight positive pressure and prevent air from entering the system. This happens for a short amount of time only.

You really need to ALWAYS put a vacuum pump on the system for it to work properly when recharged. Over the past two summers I've repaired the A/C on probably about 75 vehicles. Yes, the shorter the period of time the system is open to the atmosphere the less moisture that gets in the system. However there have been systems I've dealt with where we were in a hurry and only put a vacuum pump on it for 15 minutes or so, and then had to go back and put the pump on again for 45 minutes, because the air wasn't blowing out cold enough.

I might add, this was in New York City. Our summers are hot and humid. I still would NEVER suggest replacing a component on an A/C system and then proceed to charge it without vacuuming the system to 30" for a good 30-45 minutes, and then letting it hold the vacuum for another 30 minutes or so to ensure no leaks.

I must have been lucky. My compressor locked up 2 years back and I changed all the related parts but not having a vacuum, I put it back without evacuating the system. It has blown cold and not given any problems untill the compressor hose developed a bubble and popped a few months ago. Again I didn't vacuum it and it works fine.


I'm not saying follow my example.


I would have vacuumed it knowing better and having a pump.

I'm an AC guy, have a TACLA license, that's a contractor license for HVAC in the state of Texas for those that don't know. R134 will cool as well as R12 when you are in motion. R12 is next to impossible to get now. Discharging to atmosphere is against the law, but by far the easiest and cheapest way to evacuate your system. The parts guys, won't know or care if you "cleaned" your system proffesionally. You don't have to pull a vacuum, I never have on car/truck system, always do on residential or commercial systems, to get moisture out. Just charge it with a quick charge can until the gauge shows correct charge. Change everything but the condensor and hoses when you open your system. Any questions email or pm me and I will tell you how to do this safely, legally, and quickly. By the way if you get the kit from the parts store hook the hose to the high pressure side, put the other end in water and that will keep the tree huggers from reporting you.Edited by: winchster

Yeah, discharging the system into the atmosphere also means you have to breath the stuff. Neither R12 or R134a is good for you. R134a is worse... been known to cause testicular cancer and fun respiratory problems. R12 AFAIK is just respiratory problems. If I ever know that a system is leaking I just leave the shop until I'm convinced it's done and been properly ventilated. I like my various internal organs to stay healthy, thanks.

You pull a vacuum on a car/truck for the same reason in a residential or commercial system, to get the moisture out. You ALSO do it to get the air out, which displaces refrigerant and makes the system less effective (very easy to prove using a few engineering formulas). The moisture is the biggest enemy. Perhaps the dry heat in Texas has allowed you to get away with this. In New York City (granted, much more humid there) charging the system without vacuuming it first will result in a car that doesn't blow very cold at all, and a dissatisfied customer.

You may be certified, but if that's your technique, please don't touch my A/C system. I'll do it myself, thanks. Certification only means someone says you know how to do it, doesn't mean much else. I've come across too many ASE certified mechanics who barely know the box end from the open end on their wrenches.

Ted,


The only dry heat in Texas is in west Texas. The only time the atmosphere is dry here is right after a cold front has pushed through.

i think that he meant that putting a vac on the system is more important on a residential/commercial system. this makes sense as either of those systems if vented to atmosphere have a lot more volume in the lines and components to displace over the relatively small system on vehicles. we appreciate opinions but we could have done without the last paragraph in the last post. we're here to learn not step on toes....okay i'll climb down now

QM,

When I was in Texas a few weeks ago it felt dry in comparison to the NYC heat I dealt with all summer! http://www.dieselplace.com/forum/smileys/Big Smile.gif The 106 in San Antonio was much more bearable than 85 on Long Island.

Then again, my senses may just be off. Wouldn't be the first time.

The cans of "air" that they sell for cleaning computers and stuff are just R134A. It used to be R12 when they still used it.


They can sell that in Wisconsin but not in a can to put in a car unless you have a license.http://www.dieselplace.com/forum/smileys/Confused.gif

Ted, since you seem to be the man on A/C systems, what's the difference in the lubricants for differenct A/C systems, is there any danger of using a different one from the manufacturers suggestion? Is there a 'universal' one that will work if you don't know which you need? And what do you think of Freeze 12, its supposed to replace both R12 and R134a freon, is it as good as they say?

Oils/lubricants in a/c systems are a little different. The engineer that I talked to, said that he perfers PAG oil in mobile systems. There is Ester (POE) oil on the market too. From what he described, the POE does not do as well because of the viscocity. POE works in all the stationary-electric driven equipment that I work on daily. Difference between stationary-electric, and engine driven a/c systems is the speed in which they turn. From what he said, that POE has a much higher failure rate than that of PAG. PAG is what Carrier Traniscold used in my A/C system on my van.


One other thing about oils in a/c systems. I don't know what parts houses do this, but they sell these oils, and people add them when they need or not. Do you add oil "just because" to the crankcase without pulling the dipstick? If you can have too much oil in an A/C system, and it's counterproductive. It inhibits heat transfer, and increases your chances of liquid slugging in your compressor, a sure-fire heart-attack for your compressor. In stationary electric systems, I will pull the compressor and dump the oil to see what's in it. Unless it's had a substainal leak that has lost an amazing amount of oil, I will see what oil is in the crankcase of the compressor. If it is low, then the oil is out in the system somewhere. I will reduce the amount of oil in the new compressor to not less than 50% of the oil charge called for in the crankcase, and install in the system. So if you have a compressor that calls for 20oz of oil, and only has 10oz in it - where's that other 10oz at . . . out in the system somewhere, (unless you see a good leak somewhere) If you put 20oz in with new compressor, you will have 30oz in the system total. Know what I mean?

So I guess to check the oil and see how much is there you have to evac the system and dissassemble the compressor, all I wanted to know, thanks!


So what about this Freeze 12 stuff? is it any good?

Since vacuuming the system after an evac is so critical, what would stop a guy from using the vacuum pump in the truck to do that? Surely you could rig something up to pull a vaccum on the system and just let her idle for a half hour or so.

I'm not the man on A/C systems nor do I claim to be, I only know what I've dealt with, but I DO know how to make a system blow out ice cold.

There are varying kinds of oils that you can use, and whatever oil you use needs to be compatible with whatever refrigerant you use. What refrigerant you use depends on the shop, essentially. Most that I come across have switched over to using R134a (including the one I worked at). We use Ester oil, however depending on what we're doing we don't always add oil to the system. The compressor is supposed to hold whatever sum of oil is required for lubrication in its sump (built-in). So, when putting in a new compressor it's very important to add oil as (theoretically, anyway) most of the oil should be in the compressor. When just changing o-rings and doing a recharge it's less of an issue. Yes, you can put too much oil in a system and that will displace the refrigerant causing less than optimal cooling. My friend did this on his minivan when he changed out the compressor because he didn't believe the specified amount of oil was enough. So now it doesn't blow out as cold as it should, but it still works. When you buy a compressor it will usually have a sticker on it saying how much oil is required. Compressors have different ways of having the oil added to them. On the compressor on my truck ('97, so I believe it's a Sanden or Sanden equivalent) I had to turn the compressor by hand to get it to take in the full amount of oil it needed (I believe it was 8 oz). It is common to ahve to do this.

I have never used Freeze 12. I have a friend who uses it exclusively at his shop because he doesn't like converting systems over to R134a, and he says that it blows out nice and cold. So apparently it works, but like I said, I couldn't tell you one way or the other from first hand experience. I have heard great things about R406 (supposedly cools better than R134a OR R12), but I've never used it, either.

The o-rings you're supposed to use for any system are different, but compatible to a certain extent. For example I've converted many cars to R134a without changing out all the o-rings and haven't seen the systems leak because of that. Usually something else will leak first.

Also, as I've mentioned before, I think it's important to put dye in the system whenever you do a recharge. That way if/when there's a leak, you'll be able to find it much easier.Edited by: tdupuis

sounds good, thanks


so what about using the trucks vacuum pump to evac water vapor from the system?

TDG,


If you've ever seen the one time fill cans with a r134a low pressure connector, you could cut the hose and put the trucks vacuum line into it. Pulling ~25 "Hg it should evacuate the system in a minuite or two. I think I'll try this next time I have to open the trucks A/C system to the atmosphere.

Theoretically it COULD be done, although it's not something I've ever tried before. We always suck the system down to 30" for a good long while. 1-2 minutes isn't enough, try 15 minimum. Also, if you only pull from the low side (where you add the freon) you're going to have a much slower time evacuating the system because what's on the high side has to be pulled through the compressor or the expansion valve. We vacuum from both sides.

Personally, I'd stick to the external vacuum pump, but theoretically, yes, your plan would work. Better than no vacuum, but not as good as a proper vacuum pump designed for the task.

Gotta give ya credit there TDG, you're always thinkin'! But, no, that's not going to give you the desired effect of a full vacuum in the system. Yes, you will pull down the system to 25" of vacuum, if your pump is working well on the truck. However, you've got another 5" of vacuum to go to make sure that all of the air is out of the system. That air in the system translates as "non-condensables." Pure refrigerant is what you are after in the system. Refrigerant will condense and evaporate properly when it's the only thing in the system. When you introduce water vapor and any amount of air, those products will not condense in the high side, thereby driving up the high side pressures. High side pressures are already sky high in a mobile a/c system at idle with little air flow, let alone adding air to drive up the pressure even higher.


Air is not the only thing that you will be fighting either. Moisture would be the other ingredent too. Water vapor WILL NOT get out of the system at a 25" vacuum. Water will not boil off until you get a vacuum down in 30" range. Actually, we don't even go by the inches of vacuum in the refrigeration trade, we use what's called microns. It's a gage that measures the level of vacuum at 30". You may be at 30" of vacuum all day long, but if you are at 10,000 microns, you ain't doin' didly. In low temp refrigeration, we like to see 500 or less microns to insure that there is no water vapor, non-condensables, or for that matter, leaks in the system. You can tell real fast if you have a leak in a system with a micron gage, because it will climb very fast, when your mechanical gage would still there at 30" for the next week or so. I was able to pull down to 700 microns very well with my van, with about who knows how much rubber hose (porous), and that infamous shaft seal. I thought that was excellent all things considered.


Now, bear in mind, if you are swapping really quick a compressor in and out, (like the system is only open a minute or less) and it's not completely evacuated, you will still have some out-gasing of refrigerant in the system providing a small amount of positive pressure. This will help the contiminates stay out.


The long and the short of it is: to do it right, with a real vacuum pump. If you do otherwise, that's up to you.

Yes, the correct way is to do it with a vacuum pump as I've mentioned before, but I think that TDG is looking for a low-cost method that may not be perfect or achieve ideal results, but would do the job, in true shadetree mechanic style. http://www.dieselplace.com/forum/smileys/Big Smile.gif

Other thing to keep in mind: many A/C shops will suck down the system for you for not much money and then just allow you to charge it yourself. I know several people who do this practice as they don't wish to invest in a proper vacuum pump, but do wish to do their own A/C work.

The parts guys, won't know or care if you "cleaned" your system proffesionally. You don't have to pull a vacuum, I never have on car/truck system, always do on residential or commercial systems, to get moisture out.


I guess as long as you don't come to the stores I worked at, They do care when you want to get another A/C compressor exchanged for free. TRUST ME on this one. you have to be able to show some kind of flushing of the system and other parts replaced ie.. Dryer... oh course thats here in southern OK.

we appreciate opinions but we could have done without the last paragraph in the last post. we're here to learn not step on toes....okay i'll climb down now


LUPEY6.5 do we feel better now ??

The guy was asking for CHEAP ways to do this. He obviously had no access to a vac pump. I was just making suggestions. I also NEVER suggested breathing freon, if you will note I said you could discharge it through water, thereby keeping yourself from killing yourself. Pulling a vac is by far the preferred method, if you have access. To QM and TDG, yeah you could use your truck to pull a vac, pulling 30" is a "perfect" vac and will only occur with a really nice, expensive professional pump.
To all those that doubt the level of humidity present in DFW, I challenge you to go to the national weather archives and look. It's humid here too guys. http://www.dieselplace.com/forum/smileys/Approve.gif
Bowtie, If you can show you bought all the other parts, they usually won't make you prove you cleaned it unless your a horses but, at least we didn't in the stores I worked in. (Long time ago though)

Bowtie, If you can show you bought all the other parts, they usually won't make you prove you cleaned it unless your a horses but, at least we didn't in the stores I worked in. (Long time ago though)


Correct untill you show up a 2nd or 3rd time then it rasies a few flags.

I had the opportunity to try out some of this stuff.


http://www.dieselplace.com/forum/uploads/1E5_acdischarge.jpg


Discharging into a gallon of water worked well. Not a puff of gas.


http://www.dieselplace.com/forum/uploads/653_acevac.jpg


Where the red loom goes into the blue hose, you can see my vacuum attachment. I let the truck pull a vacuum like this for 25 min. then dumped a gas/oil mix into the system and one can. It blew colder than it ever has.


Edited by: quantum mechanic

What were your pressures like before and after on the high and low sides?

I lost my high side attachment. The clutch on the compresor was shot so I could only check it not running. The lowside was 90 psi not running.


I've been in this truck a few times and it has never blown cold, cool, yes, not cold. It was cold and my old man said so as well. It was an improvement. I couldn't change the orafice, it was locked tight and even with disassembling the front clip it wouldn't budge, just bend.

Must be pretty toasty there for a 90 suction pressure and the compressor not running.


Just an FYI, the pressure in the system while not running, will only indicate what the temperature of the system is. The pressure of the refrigerant will directly correspond with the temperature of saturation. Example 33#=35°F. The only time you can use the pressure as any kind of indicator is when the pressure in the system is below the saturation pressure. Meaning, if the temperaure of the evaporator coil is 100°F, (sitting engine cold, parked, not running,) and the pressure gauge reads 50# of pressure, that would indicate, you may be low on charge, because it's way too low.

It was 95*F yesterday while I was working on it. Thanks for the heads up though...I love learing something obvious I didn't know.

I anyone tries to evacuate a home A/C system by using the compressor to pump it down you are asking for trouble. With a vacuum on the system you create a chance for arcing in the compressor motor due to less resistance for a arcover. Many of the installation manuals warn against this just for that reason.


A automotive system or home system will outgass for a fair amount of time preventing moisture from entering the sustem. If you plug the line and make sure it doesn't breath in you should be ok without evacuating the system. By plugging the line solidly it will maintain a very slight positive pressure to prevent the breathing.


On most GM sustems there isn't a sight glass to go by so a measured charge is the best way to do it. There is a label under the hood to tell you how much to put in it. A alternative is to check the temperature of the top an bottom of the receiver/dryer and they should be the same temperature. It needs to settle down a little before finishing off the charge.

Everytime I have to replace a condensor, after startup, I use the compressor to pump the system down. Done it thousands of times, no problems. You shut the liquid line and pump until the suction line starts to freeze, then you close it, kill the electric to the condensor and you have succesfully evacuated the system back to where it started.