Recovering - or rather Transfusing Refrigerant from one car to another... - PeachParts Mercedes-Benz Forum

nhdoc · #1 06-21-2006, 08:56 AM

I have an AC system which has R12 in it and one which does not. The one with R12 is not functioning properly and ordinarily I would bring it down to a local shop where they would "recover" it (i.e. steal it), then charge me to refill the system after I finished up working on it...so here's my thought...why can't I connect the gauges to both systems and transfuse the R12 from the car that has it to the one that needs a charge and effectively recover it myself? If I were to carefully bleed it from the high pressure side of the donor system into the low pressure side of the recepient system couldn't I get most of the charge to move from one to another? What am I missing?

gmercoleza · #2 06-21-2006, 09:07 AM

When hooking up the hoses, there will be a transfer of air (and likely moisture) that resides in the hoses which will contaminate your supply. Also, it will be difficult "forcing" the refrigerant into a system that does not have vacuum pulled on it. Finally, you would need hoses hooked up to both high AND low sides on both cars in order to overcome the expansion valve and ensure you get all the refrigerant out of there, and I don't know of any manifold gauges or hoses that have 2 high and 2 low connections.

nhdoc · #3 06-21-2006, 09:41 AM

I don't see why I need to connect a low side to the donor car or a high side to the recepient car...I was just planning on connecting the high side to the donor car's high pressure line, the "fill line" to the low pressure side (suction) of the recepient and start both cars and run both compressors. The natural flow will be from the high side to the low side. Sure, I won't get every drop out but I would guess I would get most out...

I think I can evacuate the recepient car before I connect the two and start from a vacuumed system on that side and purge the air from the hoses before connecting the low side...that would fill the hoses with refrigerant and eliminate most of the moisture ladened air from being transferred.

gmercoleza · #4 06-21-2006, 09:47 AM

The high pressure line is also called the liquid line. It contains HOT liquid. Touch the high-side line when the system's running and you will understand why. Now think about the effect of HOT liquid being shot into the suction line at 250 psi just a few inches from the running compressor. Your reed valves will turn to shrapnel. That's why I referenced the expansion valve. The refrigerant cools as it expands past the expansion valve and evaporates inside the evaporator.

Ideally you would want to pull a vacuum on one system and hook up high-side to high-side, low-side to low-side, and allow the evaporation process to move the refrigerant, along with maybe a little heat (systems not running). But like I said, I can't think of any device or hose configuration in existence that would allow you to do that...

Richard Wooldridge · #5 06-21-2006, 09:50 AM

Hi there,
It sounds kind of wild, but I don't know why it won't work ok - I'm not sure that you want to tap the high side, though, especially with the donor car running. At the very least, transfer all you can get before starting the donor car to avoid slugging the compressor on the other car with liquid freon. Let us know how it worked!

nhdoc · #6 06-21-2006, 10:07 AM

There's actually hot, high pressure GAS on the outlet of the compressor high-side, not liquid. The liquid doesn't form until after the condensor does it's job - hence its name. That's why I would draw the high side gas from the donor and bleed it into the low side of the recepient...I wasn't planning on just opening the valves full blast, but regulating the pressure to maybe 60 PSI on the outlet of the donor car...that would be enough to go from high to low.

gmercoleza · #7 06-21-2006, 10:23 AM

Hmmm...

I missed the part about pulling the refrigerant pre-condenser. Also, you didn't say anything about regulating the pressure - you said you would just connect the hose and turn the systems on. Still, I'd be worried about the temperature of the refrigerant, even if it is gas. That liquid line gets REALLY hot. Something about channeling hot gas into the cold suction line just doesn't sit well with me.

But who knows - it might work.

nhdoc · #8 06-21-2006, 10:30 AM

I did say "If I were to carefully bleed it from the high pressure side of the donor system into the low pressure side of the recepient system..." in my original post...it probably wasn't completely clear that I meant to throttle the pressure through the valves on the manifold...

it seems there is only one way to find out if this will work and that is to actually try it...I'll report back and let you know how it goes.

I'll probably start out by just running the recepient car's compressor, like Richard Woolrich said above, and trying to "suck" out as much vapor as possible from the donor without running its compressor...it would seem this would work as well as charging from a can of refrigerant. I'll see how that goes then try the "power transfusion" if I can't get enough out initially. The principle seems to be to get the gas to move from higher pressure to lower pressure, but one of the compressors has to run in order to get past "equalized pressure". I'm just not sure if I need to actually run both car's compressors...it would go faster that way I am sure, but it may not be necessary.

Cressida · #9 06-21-2006, 02:10 PM

You can make the transfer just fine as you've described.

Just be sure you pull a good vacuum before you start and purge the lines of air. Really a good way of recovering most of the R-12.

Another way to recover most of your R-12 is to get a cylinder (like a 20lb BBQ tank) and install the proper fittings so that your guages will hook up to the tank. Then put the tank in your freezer overnight and it will pull all of the liquid out and most of the vapor too. Just make sure you don't have any air in the tank or lines. You will need a vacuum pump to get a good vacuum on the tank before using it.

deanyel · #10 06-21-2006, 06:25 PM

Wear a hockey goalie uniform when you do it - if you one have around.

Kuboske · #11 06-21-2006, 10:32 PM

It appears you had your mind made up. And the how to all ciphered out before hand. So why ask permission? You Rebel you knew you were going to do it anyway!

One thought, when a reclaimer is used the refrigerant is filtered to remove any contaminants there maybe. And there is a small screen somewhere in the system( At least on all U.S cars. I just assume Mercedes is the same. If not, forgive my assumption.) that can become clogged.

I think the Goalie outfit is a good Idea. Maybe you can borrow Jason Vorhies. Its a little beat up but its better than nothing! : )

#12 06-21-2006, 11:25 PM

They used to sell charging scales that you could draw a vacum on and measure the amount removed. They looked like a graduated glass cylinder with R12 fitings on the top and bottom, with a hook on the top to hang it. Some shops used these to dole out R12 for individual repairs, because the techs were very liberal with it. Using it to flush systems, fill tires, friends cars, ect.

nhdoc · #13 06-22-2006, 06:54 AM

Quote:

Originally Posted by Kuboske

It appears you had your mind made up. And the how to all ciphered out before hand. So why ask permission? You Rebel you knew you were going to do it anyway!

Well, actually, I didn't have my mind made up, I was wondering if anyone had any good reasons why it wouldn't work...none were presented. I figured I knew enough about AC systems to figure it out, but on the off chance someone who knew more than me said "XXX is why you can't do it" and that made sense I would have to reconsider my options. Since those who contributed couldn't come up with a reason it wouldn't work I have decided to give it a try...no hockey gear will be used, but I might wear safety glasses.

nhdoc · #14 06-22-2006, 06:55 AM

Quote:

Originally Posted by John Holmes III

They used to sell charging scales that you could draw a vacum on and measure the amount removed. They looked like a graduated glass cylinder with R12 fitings on the top and bottom, with a hook on the top to hang it. Some shops used these to dole out R12 for individual repairs, because the techs were very liberal with it. Using it to flush systems, fill tires, friends cars, ect.

Interesting...I was counting on just using the sight-glass on the recepient car to know when it was full...that's always proven to be adequate on R12 systems in the past.

gmercoleza · #15 06-26-2006, 11:07 AM

Yes, sight glass method on an R12 system is perfectly acceptable. When topping up my 300E with R12 every year (it needs a can every year) I don't even use the gauges anymore, just hook up and fill until the sight glass is *almost* clear.