All of the How-to's online seem to deal with systems that are already empty of R134A. My system is full, and I need to disconnect my lines to replace the head gaskets.

It is my understanding that I need to reclaim the R134a in my system. I believe this is done my attaching gauges to the high and low side AC lines, attaching the vacuum (yellow) line to an empty refrigerant tank, and attaching a vacuum pump to the other valve on the tank.

I just want to make sure I understand all this before I buy the system. The truck is immobile right now (partially torn down), and while I'd rather take it to someone or have someone come do the job, neither are possible.

I just want a little clarification on the procedure... The tank I'm looking at has a red and a blue valve. I'm going to attach the vacuum to the blue valve and the gauge's yellow line to the red tank valve. I'm going to close the red valve and pull vacuum on the blue side for about 30-60 minutes. Once done, I'll close the blue valve, and open the red valve. I now have negative pressure to suck the R134a from the system into the tank.

The gauge set also has a red and blue line. The red going to the AC high side, and the blue to the low side. With both closed, I open the blue side, and the negative pressure from the recovery tank will pull the R134a from system. When both red and blue gauges read zero, the system is empty and can be disconnected, which entails closing the red valve on the tank, closing the blue valve on the gauge, and disconnecting all lines.

After that, I can disconnect the vehicle AC lines.

When I'm done, I reverse the procedure to refill the AC system. This time, I draw 30-60 minutes worth of vacuum on the vehicle AC system via both the red and blue gauge valves. When both red and blue gauges read negative pressure, I close both valves on the gauge, disconnect the vacuum pump from the yellow line, and connect the refrigerant tank red valve to the yellow line. I open the red valve on the tank, and the red valve on the gauge. This will fill the system with my recovered R134a.

Is there anything I'm missing in all this? I'm a little surprised that for $260, I can buy the gauges, vacuum pump, and tank. The "mobile AC recharge guy" (who doesn't come to my area) quoted me $450 (for two trips, one to evac the system, and another to fill it).

 

You have 134 in your system, not R12 so it is already more environmentally safe. If you were running a business and opening your systems up to do regular maintenance I would recommend purchasing recovery equipment. As it is you are just concerned with one vehicle with maybe a couple pounds of R134 refrigerent. Just crack a line and slowly release it to the atmosphere. If in a shop open the windows and doors to let it outside. When you complete repairs take the vehicle to a repair shop and have it evacuated and recharged.

 

As my cheap Uncle Scrooge once said, "Leaks happen...."

 

There's really no good way to recover the refrigerant without a machine. To do it the way you describe, the cylinder would need to be packed in dry ice. That's a lot of screwing around to save a couple of pounds of R134a.

Ideally, you would call a refrigeration company to come onsite and recover the refrigerant from the system.

I would never suggest that you vent the refrigerant because that's illegal and not very "green", but if you installed your gauge set and one of the valves was cracked open slightly....

 

I don't wish to be ungrateful for the suggestions provided, but I'd rather not vent my system to atmosphere.

I have two reasons for this. Firstly, it's illegal. I don't much care about the effects of such a small quantity of gas, but I'd rather stay within the law when it's within my means. Secondly, I'd rather have the ability to do this type of service myself. Even if I vent it, I still would need to have it recharged (or risk burning up the compressor), which would cost me $225 (if I could convince the mobile guy to drive all the way to my house), or a little less if I drove it to a shop for the recharge. For about the same money, I can own the equipment.

 

Why would it need to be packed in dry ice? And what exactly would this "machine" do that the vacuum pump would not?

 

Cooling the recovery cylinder would allow the proper pressure differential to draw most of the refrigerant from the system. Connecting a cylinder (under a vacuum) to the system at room temperature will only allow a small amount of refrigerant into the cylinder before the pressure equalizes.
Doing it this way has been discussed at length here:
Automotive AC Information Forum - ACKITS.COM Do a search for "dry ice" if you are curious.

A recovery machine actually "pumps" the refrigerant from the system into the cylinder. However, to reuse the refrigerant you would need a recovery/recycle machine. These are out of the budget for most DIYers, costing in the $1000-3000 range.

Edit: What you describe doing with the recovery tank and vacuum pump would draw the refrigerant from the system, into the tank, into the vacuum pump and out the pump exhaust. In effect, a vacuum assisted leak. The blue valve is open to the top of the tank (gas), the red valve has a tube that extends to the bottom of the tank (liquid).

 

While it is illegal to knowingly discharge R134a into the atmosphere since about 2004, it is not uncommon for items such as compressed gas air cleaners to contain R134a and you most definitley discharge it into the atmosphere when cleaning computers and circuit boards etc.

Now if you were working in a shop and were dumping the stuff out in volume everyday you would be nuts, but one person on one job isnt going to bring the sky down or the EPA knocking on your door.

 

Nope... I draw the vacuum on the tank first, before I connect it to the AC gauges. This gives me a large negative pressure reservoir. I then close the valve, disconnect the vacuum, and connect the tank to the gauges. Then I reopen the tank valve and "suck" the refrigerant from the system.

I'll check out your link. Thanks!

 

Oh, Gotcha. I misunderstood.
Still, doing it that way will only recover part of the refrigerant unless you cool the cylinder to condense the refrigerant into a liquid.

 

Or... I can vacuum the tank, then vacuum the coolant from the system with the output connected to the tank. This would form the "pump" you mentioned earlier and solve the pressure equalization problem, I think.

 

No. A vacuum pump isn't suited for making pressure on it's outlet.
However, you could use a compressor from a refrigerator or AC unit and make a recovery pump. That's the type of compressor that my R12/R134a handler uses.
I didn't think to mention that earlier.
You would need some sort of oil separator in the system to keep oil out of the tank.