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Static pressure in recovery tank too high by 10 psi or so... how can I bleed air?

Leggie on Sun June 17, 2012 4:11 PM User is offline

Refrigerant Type: 12

Somehow, air managed to get into my recovery tank. There's only 3 lbs of R12in 30 lb recovery tank. Is there anyway to salvage it?

buickwagon on Sun June 17, 2012 7:06 PM User is offline

In theory, if you put the tank in the freezer for a few hours at -40° or so, the vapour pressure would be less than 1 atmosphere. Therefore all gas would be air and all refrigerant would be liquid even if you opened the valve. You could then remove the air with a vacuum pump. At about 200mmHg the refrigerant will begin to vaporize, displacing the remaining air (since it is heavier than air). Monitoring the discharge with an electronic leak detector would show the moment the remaining air was purged from the tank.

If you could get it down to -200° F or so, you wouldn't need the detector, the refrigerant would remain liquid at full vacuum but the air (at least, the nitrogen and oxygen) wouldn't condense.

Note: I did say "in theory". I wonder what happens to vacuum pump oil at -40°?

I've saved hundreds on service by spending thousands on tools.

Dougflas on Sun June 17, 2012 8:53 PM User is offline

Let the tank sit for 24 hrs without disturbing it. Then open the vapor handwheel and bleed the pressure off a little at a time. Then repaet the senario. Check the temp vs pressure to see if you got all the air out.

GM Tech on Sun June 17, 2012 10:38 PM User is offline

That's how the recovery machines do it.......bleed off the air that is trapped at the top of the tank...

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

mk378 on Mon June 18, 2012 9:54 AM User is offline

The vapor space of the tank contains a mixture of refrigerant vapor and air, so you're always going to bleed a mixture and lose some refrigerant. Like buickwagon said, getting the tank cold will reduce the partial pressure of the refrigerant and improve the efficiency of the process.

An alternative is to slowly remove the refrigerant as liquid from the bottom of the tank, where it will be pure (or at least not contain air). But you have to be very careful not to completely empty it and start getting mixed gas out.

Edited: Mon June 18, 2012 at 9:55 AM by mk378

Leggie on Tue June 19, 2012 4:23 AM User is offline

Is there such thing as liquid separator that's soda can sized? I'd like to use a capillary tube to limit the flow and circulate the mixture through the separator with the bottom of separator connected to a receiving tank.

Basically, works like dehumidifier. Refrigerant is precipitated out of air/refrigerant atmosphere and liquid drained out.

mk378 on Tue June 19, 2012 10:04 AM User is offline

If you cram the gas mixture into a smaller space, it would increase the partial pressure of air while (after it cools), refrigerant would condense at the bottom and could be drawn off. So then the gas mixture is leaner in refrigerant. This would be done in a batch process-- raise the pressure as high as possible, cool as cold as possible, then draw off refrigerant, vent air(*), and repeat if more mixed gas is to be processed.

(*) In a commercial version of the process, the vented air with some R-12 contamination would go through an incinerator to break down any remaining R-12 rather than allow it into the atmosphere.

Edited: Tue June 19, 2012 at 10:05 AM by mk378

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