Automotive Air Conditioning Information Forum (Archives)

BG1 on Fri October 08, 2010 7:09 PM

Year: 1976
Make: Pontiac
Model: Firebird
Engine Size: 455
Refrigerant Type: R134a

I have a 1.5 cfm deep vacuum pump and a recovery cylinder, Should I be able to recover most of the refrigerant? How long should I let the pump pull a vacuum on the cylinder?

Dougflas on Fri October 08, 2010 7:54 PM

No can do. If you want to try something, evacuate the tank. Put it in ice bucket and get it cold. Heat engine but do not run AC. Connect gauges to the vehicle. Connect middle hose (yellow) to tank but do not open vapves on tank. Open low side hand wheel of gauges. Purge yellow hose at tank. Open tank valve. Refrigerant will transfer to tank. You can heat the components of Ac system with hair dryer to help transfer refrigerant.

BG1 on Fri October 08, 2010 8:46 PM

You said "No can do" so you don't think this will work? I thought it might be worth a try but appreciate information on it. Has anyone done this successfully? Has anyone tried it and found out that it does not work?

TRB on Fri October 08, 2010 11:30 PM

Getting popcorn and waiting for the engineers to have a go at this one.

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When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

Cussboy on Sat October 09, 2010 1:06 AM

Quote
Originally posted by: TRB
Getting popcorn and waiting for the engineers to have a go at this one.

I HAVE recovered refrigerant successfully a few times in the past few years, mostly R-12.

I have a metal cannister, about 12 inches by 4 inches diameter, with a shut-off and flare valve. I attached it to my gauge set (middle fitting), attached high side hose to the vacuum pump, and low side hose to low side fitting, and had the cannister sit in a dry-ice-alcohol bath in a bucket. I pulled a vacuum from the cannister (only) then closed it off and opened the cannister to the low side, and my refrigerant all went into my cannister for future use. The refrigerant comes over, condenses to liquid, so the canister continues to be at vacuum, so refrigerant continues to come over. Then I re-added it after the repair.

The cannister can have either a flare or an Acme R134a fitting, doesn't matter as long as it fits your gauge set.

By the way: I'm a chemist, not engineer.


Edited: Sat October 09, 2010 at 1:07 AM by Cussboy

Dougflas on Sat October 09, 2010 2:43 AM

when i said, "No can do" I was referring to use the vacuum pump as a recovery pump. One thing I left out of my previous answer was the need for filtering the recovered refrigerant.

NickD on Sat October 09, 2010 7:33 AM

I got involved with recovery machine design somewhere back in the mid 70's when it was rumored that the EPA would demand recovery due to those couple of smoke cracking profs at UCLA. Can't use a conventional vacuum pump, for one thing the impellers are soaks in vacuum pump oil and the outlets are not designed for those kind of pressures. Can try it and watch it blow apart.

Recall did finding a refrigerant pump with a dry impeller, but that was like 35 years ago, memory is not that good to recall a make and model, but there are such a thing as a refrigerant pump designed explicitly for that purpose. In sneaking around looking at competitive units at the time, were just using standard automotive accumulators for the filter, that in my opinion wasn't very good.

Anyway, at that time, the EPA elected not to make mandatory recovery, I dragged my feet on this project that was good for my company, as other companies went bankrupt with warehouses full of recovery machines that were junk. Why recover when you don't have too? It took a man with integrity like Al Gore to put this into action, and overnight at that.

I have used my vacuum pump for such weird things as pulling the oil out of an engine dipstick hole, but have two tubes soldered into a two quart Mason jar. One inside the dipstick hole, the other to the pump. But the oil never goes through the pump, just ends up in the bottom of the container. Can't do that with refrigerant, its a gas, the pump has to between the source and the tank, maybe with an accumulator in between.

The theory of routing AC refrigerant directly into a tank is not exactly rocket science. If the tank is held, say at -15*F the refrigerant within it will be in a liquid state at 0 psi pressure. The refrigerant in the system at the system at 140*F will be a gas at around 220 psi pressure that will flow into the tank. Kind of a slow process due to heat transfer and stabilization time, but it works. There is an inherent degree of filtering as the refrigerant is going through a distillation process, most of the crap is left in the system. Main reason for adding an accumulator is a meager attempt to gather some of the moisture.

TRB on Sat October 09, 2010 10:31 AM

Quote
Originally posted by: Cussboy
Quote
Originally posted by: TRB
Getting popcorn and waiting for the engineers to have a go at this one.



I HAVE recovered refrigerant successfully a few times in the past few years, mostly R-12.



I have a metal cannister, about 12 inches by 4 inches diameter, with a shut-off and flare valve. I attached it to my gauge set (middle fitting), attached high side hose to the vacuum pump, and low side hose to low side fitting, and had the cannister sit in a dry-ice-alcohol bath in a bucket. I pulled a vacuum from the cannister (only) then closed it off and opened the cannister to the low side, and my refrigerant all went into my cannister for future use. The refrigerant comes over, condenses to liquid, so the canister continues to be at vacuum, so refrigerant continues to come over. Then I re-added it after the repair.



The cannister can have either a flare or an Acme R134a fitting, doesn't matter as long as it fits your gauge set.



By the way: I'm a chemist, not engineer.

You're pulling a vacuum on a cylinder. They way I read the question was one wanted to use a vacuum pump to reclaim refrigerant.



-------------------------
When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

BG1 on Sat October 09, 2010 2:14 PM

I am wanting to pull a vacuum on the cylinder and then try to recover the refrigerant. I am not trying to use the vacuum pump to draw the refrigerant from the system.

TRB on Sat October 09, 2010 3:27 PM

Cussboy has explained that process and this same process has been mentioned a few times int he past on the forum. Never tried it my self so I can;t comment on how well it works.

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

NickD on Sun October 10, 2010 8:16 AM

Use to have service valves on these things, actually still have these on my old York. Can jury rig one, or maybe they even sell one someplace. Something you can attach directly to the service ports with a closed valve and means to attach your red hose manifold gauges to. Just cracking that valve open for a half of an instant will purge it.

So with your red hose connected to that valve, yellow to the tank, blue to the vacuum pump. with that extra service valve closed, reservoir tank valve opened, red valve open, vacuum pump valve opened, can not only draw vacuum from the tank, but clear up to that added valve.

How long? depends upon how long of a nap you want to take, but at least 45 minutes, you do not want to contaminate your precious refrigerant with air. Can pack your tank with salted ice, haul out your freezer and store the tank in there, or get dry ice. Close off your low side valve to seal off the vacuum pump, open your added external valve that gives a direct path to your tank. Again the hotter your AC system and the colder that tank, the larger will be your pressure difference.

You can see the reason for that added valve, if you just draw a vacuum from your tank, no way in the hell can you connect it to your AC system without it sucking in air, even for a fraction of an instant, then you end up with contaminated with air refrigerant, kind of worthless.

Is something about having very precise gauges and a thermometer to check the pressure of the tank against a PT chart, if the pressure is greater, you have air in the tank, and by leaving the tank in a vertical position and let it settle for an undetermined period of time, the air will go to the top and can be released from the tank until that pressure is right. But why introduce air in the first place?

Can also purge your system in outer space, won't have to worry about cooling your tank, will be far below subzero, but heating your AC system will be a problem.

Can also buy a good recovery machine. I don't seem to have a problem with recovery, with the crap the automakers are putting out today, nothing to recover. For doing other engine work, so far, always found away to work around that. When they tossed these things together, maintenance wasn't even in their vocabulary.

BG1 on Sun October 10, 2010 9:55 PM

Is there a valve that can be used in this application to connect to the ac system and to the r134a connection on the hose set? If so who would have it?

emsvitil on Mon October 11, 2010 1:50 AM

check grainger.com

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Ed
SoCal

BG1 on Tue October 26, 2010 12:31 PM

According to the digital scale I have it indicates that all the r134a went into the recovery cylinder, would this be a correct assumption to go by the weight of the cylinder before and after? To put it back in the car ac system which port on the recovery cylinder do I need to use? There is a vapor and a liquid port. I understand that the cold cylinder helped the refrigerant leave the ac system and go into the recovery cylinder but what causes it to go the other way?

Dougflas on Tue October 26, 2010 12:51 PM

use the vapor unless you're thoroughly versed on charging procedures. You can place the cylinder in a wqater bath to increase its pressure. That will make it "go the other way". Also, after you have at least 50% charge in the system, the compressor can be engaged and the refrigerant will be "sucked" into the system from the tank. Make sure you use filters.

BG1 on Tue October 26, 2010 2:15 PM

Thanks, I put the cylinder in a large pot of warm water and its got the refrigerant moving now.