AC system "open"
03-28-2019, 08:11 AM
#1
Three Wheelin'
Thread Starter
AC system "open"
getting ready to install a replacement rear AC evaporator, and wondering how long I can leave the system open before recharging.
I would prefer to replace the evap and then recharge a few days later, but wonder if that is a bad idea? drier is not that old and don't
want to ruin it.
if it is imperative, I will find the time to do everything in one shot, but is it OK to leave a system open for a day, a few days, a week??
I would prefer to replace the evap and then recharge a few days later, but wonder if that is a bad idea? drier is not that old and don't
want to ruin it.
if it is imperative, I will find the time to do everything in one shot, but is it OK to leave a system open for a day, a few days, a week??
03-28-2019, 10:17 AM
#2
Three Wheelin'
Thread Starter
don't believe I was clear with my first post: I would properly evacuate the system, replace the evaporator, and the lines would be immediately reconnected.
the system would be open for no more than 15 minutes for this repair. then, a few days later, I would do a proper recharge. would those 15 minutes of the system
open induce enough moisture in the system to compromise the drier? I was not intending to leave the lines completely open for a few days.
the system would be open for no more than 15 minutes for this repair. then, a few days later, I would do a proper recharge. would those 15 minutes of the system
open induce enough moisture in the system to compromise the drier? I was not intending to leave the lines completely open for a few days.
03-28-2019, 10:26 AM
#3
Rennlist Member
I doubt it: When you pull a vacuum it does cause the residual water in the system to boil out, this is why it sometimes seems to take awhile to get that last bit of vacuum in the system. This should pull out any residual moisture, one good way to check is to draw the vacuum, leave it on for a bit, then after turning the pump off see if the pressure goes up a bit. That's usually water boiling out, then pull more vacuum.
Dryer should be swapped when there is any concern about contamination, if it's been awhile since replacement, or if the system gets a lot of water in it.
Dryer should be swapped when there is any concern about contamination, if it's been awhile since replacement, or if the system gets a lot of water in it.
03-28-2019, 01:17 PM
#4
Chronic Tool Dropper
Lifetime Rennlist
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If you are replacing the drier (as you should) as part of your effort, delay installing that drier until you are ready to evacuate. Remember to inject the oil for the drier and the evaporator as part of that effort. You'll be fine.
For those playing along at home --
The drier is tasked with removing any moisture that doesn't get drawn out by the evacuation process. It includes a bag of a dessicant that's compatible with the refrigerant and lubricant you are using in the system. The lubricant brings moisture along too, so the dessicant is grabbing from both the refrigerant liquid that passes through and the oil that's carried in the refrigerant. Whenever the system is opened to air, and when any major system component is replaced, it's good form to install a new drier. They are relatively inexpensive. IIRC the good replacement is a 944 piece, so not a diamond-encrusted 928-only specialty piece at least cost-wise.
In another FWIW, I've seen several 928's that showed symptoms of an evaporator leak when sniffed with the electronic detector around the connections at the cowl. After removal, the evaporator was fine. The actual failure mode of the aluminum evaporator is from oil contaminated with moisture that gathers in the bottom sections, becomes acidic with the refrigerant, and proceeds to eat through the aluminum. This points back to the importance of a very thorough evacuation of the system along with a new drier whenever the system is open. Remember that when evacuating the system for moisture removal, you'd really like the system and ambient conditions to be as warm as possible. The freezing point of the moisture rises as the pressure drops, and you'd like the water to go to vapor rather than to ice so the pump can draw it out. Extending the time under vacuum helps a lot. Even in the almost-tropical temps in SoCal, I'd leave the three-stage pump running at least overnight to get the system dry and empty. The vacuuming doesn't do much of anything for removing moisture from an oil-soaked drier, hence the plan of evacuating to dry, then injecting the oil, more vacuum time for final air removal, then charge with refrigerant.
For those playing along at home --
The drier is tasked with removing any moisture that doesn't get drawn out by the evacuation process. It includes a bag of a dessicant that's compatible with the refrigerant and lubricant you are using in the system. The lubricant brings moisture along too, so the dessicant is grabbing from both the refrigerant liquid that passes through and the oil that's carried in the refrigerant. Whenever the system is opened to air, and when any major system component is replaced, it's good form to install a new drier. They are relatively inexpensive. IIRC the good replacement is a 944 piece, so not a diamond-encrusted 928-only specialty piece at least cost-wise.
In another FWIW, I've seen several 928's that showed symptoms of an evaporator leak when sniffed with the electronic detector around the connections at the cowl. After removal, the evaporator was fine. The actual failure mode of the aluminum evaporator is from oil contaminated with moisture that gathers in the bottom sections, becomes acidic with the refrigerant, and proceeds to eat through the aluminum. This points back to the importance of a very thorough evacuation of the system along with a new drier whenever the system is open. Remember that when evacuating the system for moisture removal, you'd really like the system and ambient conditions to be as warm as possible. The freezing point of the moisture rises as the pressure drops, and you'd like the water to go to vapor rather than to ice so the pump can draw it out. Extending the time under vacuum helps a lot. Even in the almost-tropical temps in SoCal, I'd leave the three-stage pump running at least overnight to get the system dry and empty. The vacuuming doesn't do much of anything for removing moisture from an oil-soaked drier, hence the plan of evacuating to dry, then injecting the oil, more vacuum time for final air removal, then charge with refrigerant.
03-28-2019, 01:38 PM
#5
Rennlist Member
The drier is so cheap, and so critical to the system, Id replace it anytime Im doing a complete service on the system.
Free moisture comes out easy, captured moisture is harder...and even a tiny amount in the system has a large effect on it's performance.
Free moisture comes out easy, captured moisture is harder...and even a tiny amount in the system has a large effect on it's performance.
03-28-2019, 02:44 PM
#6
Three Wheelin'
Thread Starter
If you are replacing the drier (as you should) as part of your effort, delay installing that drier until you are ready to evacuate. Remember to inject the oil for the drier and the evaporator as part of that effort.
you'd really like the system and ambient conditions to be as warm as possible. The vacuuming doesn't do much of anything for removing moisture from an oil-soaked drier, hence the plan of evacuating to dry, then injecting the oil, more vacuum time for final air removal, then charge with refrigerant.
you'd really like the system and ambient conditions to be as warm as possible. The vacuuming doesn't do much of anything for removing moisture from an oil-soaked drier, hence the plan of evacuating to dry, then injecting the oil, more vacuum time for final air removal, then charge with refrigerant.
dr. bob> was planning on injecting oil in the evap, but did not know I should inject in new drier as well? I thought a new drier would not require additional oil? how many oz.?
and
if I follow the WSM and add 1,150 gr. of Freon exactly, does it matter what the outside temps are?
03-28-2019, 03:00 PM
#7
Rennlist Member
OK you guys got me....again. was not planning on replacing, but at 3 years old, its probably time. guessing that all driers are the same?
dr. bob> was planning on injecting oil in the evap, but did not know I should inject in new drier as well? I thought a new drier would not require additional oil? how many oz.?
and
if I follow the WSM and add 1,150 gr. of Freon exactly, does it matter what the outside temps are?
dr. bob> was planning on injecting oil in the evap, but did not know I should inject in new drier as well? I thought a new drier would not require additional oil? how many oz.?
and
if I follow the WSM and add 1,150 gr. of Freon exactly, does it matter what the outside temps are?
1150g is 1150g at any temperature.
Temperatures are a diagnosis step, not a fill one.
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03-28-2019, 11:05 PM
#10
Chronic Tool Dropper
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On putting the oil in --
On a whole-system-disassembled, I put it all the oil in the compressor, then spin the compressor by hand before letting the engine spin it, just in case there's oil in a cylinder.
For a partial disassembly/replace, follow the WSM guidance on what each component holds. Pull vacuum on the system, and check for serious leaks. Then dip the (yellow) suction hose normally attached to the vacuum pump into your measuring cup of oil. Open the hi-side (red) valve and let the vacuum draw the oil into the condenser ahead of the drier. Drain all the hoses towards the system, with air pulling slowly through to sweep up any remaining oil. Then vacuum pump to dry the system out and evacuate it before recharging.
Also -- make sure you are using the same oil type that's in the system. R12 is easy, as it's a standard mineral-oil-based lubricant. If the car has been upgraded to R-134a, you -really- want to know whats in there as the PAG and POE types don't get along with each other at all.
On a whole-system-disassembled, I put it all the oil in the compressor, then spin the compressor by hand before letting the engine spin it, just in case there's oil in a cylinder.
For a partial disassembly/replace, follow the WSM guidance on what each component holds. Pull vacuum on the system, and check for serious leaks. Then dip the (yellow) suction hose normally attached to the vacuum pump into your measuring cup of oil. Open the hi-side (red) valve and let the vacuum draw the oil into the condenser ahead of the drier. Drain all the hoses towards the system, with air pulling slowly through to sweep up any remaining oil. Then vacuum pump to dry the system out and evacuate it before recharging.
Also -- make sure you are using the same oil type that's in the system. R12 is easy, as it's a standard mineral-oil-based lubricant. If the car has been upgraded to R-134a, you -really- want to know whats in there as the PAG and POE types don't get along with each other at all.
03-30-2019, 07:49 PM
#11
Rennlist Member
You do indeed want to match the oil in the system. Most responsible people would not put PAG oil in any system unless it came that way from the factory (not 928's) or has had a complete system replacement, and PAG install. POE oil BTW is compatible with mineral oil and even R12.
Good luck,
Dave
Good luck,
Dave
03-31-2019, 02:05 PM
#12
Three Wheelin'
Thread Starter
You do indeed want to match the oil in the system. Most responsible people would not put PAG oil in any system unless it came that way from the factory (not 928's) or has had a complete system replacement, and PAG install. POE oil BTW is compatible with mineral oil and even R12.
Good luck,
Dave
Good luck,
Dave
FWIW: I replaced all the old O-rings, most of which were black. new ones are green. what is the difference with the color? are the blacks not compatible with R134a and/or newer oils?
03-31-2019, 02:15 PM
#13
Archive Gatekeeper
Rennlist Member
Rennlist Member
https://www.compressorworks.com/Uplo...%20CHANGES.PDF
Cliff notes: Just buy an assortment pack of green HNBR o-rings and use them, they're pan-compatible.
Cliff notes: Just buy an assortment pack of green HNBR o-rings and use them, they're pan-compatible.
03-31-2019, 03:07 PM
#14
Rennlist Member
Interesting discussions on oils (again). If this were 10 years ago I'd say go POE. However since that time PAG oil has gotten a lot better with double end capped versions (don't acidify with water and such, and much more chemically stable) while I haven't really seen any improvements in POE (still can be acidic). To quote:
"When POE oils (as opposed to the refrigerant) break down, the resulting chemical reaction leads to the formation of organic acids rather than inorganic acids. Instead of leading to compressor burnout, organic acids typically create a sludge that can clog small valves or cause the oil to lose its ability to properly lubricate the compressor. When this occurs, the compressor will seize." (HVAC investigators)
This is a component of POE oils. They form organic acids through hydrolysis. PAG oils are more hygroscopic, but do not form organic esters through hydrolysis. To quote:
Polyalkylene Glycol (PAG) – a synthetic oil primarily used in R-134a automotive air conditioning systems. It is more hygroscopic that either POE or PVE oils, but it does not undergo hydrolysis in the presence of water.
In terms of overall stability, the Purdue paper cited below points out that Di-Ether PAG without the hydroxyl end grouping (end capped in other words) is less hygroscopic than monoether PAG with hydroxyl end groups. It's a pretty good read.
My belief (supported by a fair bit of research out there) is that DEC PAG oils have had a lot more research than POE oils, do not react with water in the system, do not form acids that bur, out your condensers, and are overall a better choice than POE. My recommendation is that you take apart the system, flush out the oil mineral oil/POE/whatever is in there, take the compressor and condenser out, clean them both out of old oil (including draining the compressor), re-adding DEC PAG, replacing the drier, and putting it all back together with new R134a compatible seals. Then pull a nice long vacuum, verify no leaks, turn the compressor by hand to distribute any slugged oil, fill it up, and enjoy life.
Citations:
Understanding HVAC Diagnoses – Acidic Refrigerant. HVAC investigators. Retrieved from: https://www.hvacinvestigators.com/un...c-refrigerant/
Effect of moisture on POE oils: The Air Conditioning, Heating and Refrigeration news. Retrieved from: https://www.achrnews.com/articles/94...isture-on-poes
HVACR Tech Tip: What Every Technician Needs to Know About Refrigeration Oils. Parker Hannifin. Retrieved from: http://blog.parker.com/hvacr-tech-ti...igeration-oils
The performance of end-capped PAG as a refridgeration oil for HFC134a.Purdue University Press. Retrieved from: http://docs.lib.purdue.edu/cgi/viewc...0&context=icec
"When POE oils (as opposed to the refrigerant) break down, the resulting chemical reaction leads to the formation of organic acids rather than inorganic acids. Instead of leading to compressor burnout, organic acids typically create a sludge that can clog small valves or cause the oil to lose its ability to properly lubricate the compressor. When this occurs, the compressor will seize." (HVAC investigators)
This is a component of POE oils. They form organic acids through hydrolysis. PAG oils are more hygroscopic, but do not form organic esters through hydrolysis. To quote:
Polyalkylene Glycol (PAG) – a synthetic oil primarily used in R-134a automotive air conditioning systems. It is more hygroscopic that either POE or PVE oils, but it does not undergo hydrolysis in the presence of water.
In terms of overall stability, the Purdue paper cited below points out that Di-Ether PAG without the hydroxyl end grouping (end capped in other words) is less hygroscopic than monoether PAG with hydroxyl end groups. It's a pretty good read.
My belief (supported by a fair bit of research out there) is that DEC PAG oils have had a lot more research than POE oils, do not react with water in the system, do not form acids that bur, out your condensers, and are overall a better choice than POE. My recommendation is that you take apart the system, flush out the oil mineral oil/POE/whatever is in there, take the compressor and condenser out, clean them both out of old oil (including draining the compressor), re-adding DEC PAG, replacing the drier, and putting it all back together with new R134a compatible seals. Then pull a nice long vacuum, verify no leaks, turn the compressor by hand to distribute any slugged oil, fill it up, and enjoy life.
Citations:
Understanding HVAC Diagnoses – Acidic Refrigerant. HVAC investigators. Retrieved from: https://www.hvacinvestigators.com/un...c-refrigerant/
Effect of moisture on POE oils: The Air Conditioning, Heating and Refrigeration news. Retrieved from: https://www.achrnews.com/articles/94...isture-on-poes
HVACR Tech Tip: What Every Technician Needs to Know About Refrigeration Oils. Parker Hannifin. Retrieved from: http://blog.parker.com/hvacr-tech-ti...igeration-oils
The performance of end-capped PAG as a refridgeration oil for HFC134a.Purdue University Press. Retrieved from: http://docs.lib.purdue.edu/cgi/viewc...0&context=icec
03-31-2019, 09:17 PM
#15
Rennlist Member
how would I know with certainty, what oil is currently in my system? is there a test or telltale? I would guess POE since it has been working great for the past 3 years. thinking that if mineral oil does not mix with PAG I would have had some adverse symptom?
FWIW: I replaced all the old O-rings, most of which were black. new ones are green. what is the difference with the color? are the blacks not compatible with R134a and/or newer oils?
FWIW: I replaced all the old O-rings, most of which were black. new ones are green. what is the difference with the color? are the blacks not compatible with R134a and/or newer oils?
Good luck,
Dave