Engine Size: 3.2
Refrigerant Type: 134a
Have replaced entire system in the 911 except the rear lid condenser (flushed) and added two addl fan assisted condenser in the rear wheel well. All thats left to to do now is install the rebuilt compressor, add oil, evac and charge the system. Borrowed a nitrogen bottle from a buddy to purge the lines and pressure test the system before charging. Never done this before (Nitrogen purge/pressure test). What's the recommended procedure?
Add oil, close up the system, evacuate, see if vacuum holds, charge with nitrogen to 150 PSI MAXIMUM, see if nitrogen pressure holds. If you have a sniffer leak detector you can put in about 30 psi refrigerant first (this is only a couple of oz by weight), then nitrogen up to 150 psi, and sniff for leaks. Do not run the compressor with nitrogen in it.
You must have a regulator on the nitrogen bottle, set to 150 psi or less. Never use a gas bottle with no regulator, the pressure is extremely dangerous.
Finding no leaks, vent the nitrogen out, evacuate again, and charge with pure refrigerant. Ideally you'd use the manufacturer's specified weight of refrigerant, but since this is a converted/custom system you'll have to wing it. Keep track of how much you put in so if you have to recharge in the future you can use the same amount.
Purge the lines?
Thanks for the promt reply. I do have a regulator on the nitro bottle, but no sniffer. Hopefully with everything new my chances for leaks will be reduced....but who knows with 40 ft of hose, 4 condensers and a subcooler, I've got 16 hose connections in the sytem (crazy) A/C design was not one of Porsche early strong points!
My R-12 capacity was 47.2 oz. but after the mods the new capacity is unknown. So I'm looking at a total charge of 80% to 85% of an unknown. I'll be charging with sm cans of 134a and plan on adding 1 can (2 if it will take it) low side gas before starting the system and monitoring Pressures and Vent tems to optimize the charge. Not sure using small cans how to accurately track my total charge. I've read that one should figure 2 oz refrigerant loss for the charging hoses and 1 add oz loss for each full can used (cuz you can't get all of it out). Then if I have to remove any overcharge there's another variable. Lots of variables in the process.
The vacuum pump will remove the air from the car system. The only thing that might need to be purged is the yellow hose on your manifold when you disconnect the vacuum pump and connect the can of refrigerant.
Leave the nitrogen in at least overnight and see if the pressure holds steady for a more thorough leak test.
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