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Scott R's Avatar
 
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Post A/C Charging

I have converted my R12 system in my 85.5 NA, to 134A, new compressor and O rings. My problem is I vacumed the system down for about 1/2hr, but it's not taking a charge very well, it will take about 1/2 can of 134A, then slow way down. I can fill it very slowly, but it's not doing much. So far I have been charging it about two hours and only have 1 can in. My question is this: Is there something I am doing wrong? It almost seems like there is pressure or blockage in the system. Any ideas?

Old 05-21-2001, 07:40 PM
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I'd vacuum it out for 2-3 hours, instead of the 1/2 hour. This will get A LOT more moisture out and add longevity to the components. Hey, why not? Hook the pump up after your done driving and go eat dinner. Three hours will fly by, then pop a can in before you go to bed to add positive pressure (vacuum might leak a little air back in over night).

After a vacuum the system should take almost a whole can no trouble. You can try putting the can in warm water and shaking it to increase the can pressure, relative to the car system and force more in. (NOT TOO HOT, otherwise can pressure might blow it). By then you should have enough pressure for the compressor to kick in and suck the next can(s) in (just be 100% sure you're hooked into the low side line, otherwise you can blow the can up). Once the compressor is running, it will bring the low side pressure down to 30 psi, which is way lower than the can at room temperature and it will suck up the refrigerant no problem.

Good luck.
Old 05-22-2001, 02:15 PM
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How do you pull a vaccum on the system, ie: what tools do you need to acheive this. Is there a special vaccum pump and gauge for doing this? I've charged a few 134a systems but have never pulled a vaccum. The last time I charged my A/C the can became extremely cold and frosted up after a few minutes. It would only take about 1/2 a can. Could you pull a vaccum using a MityVac bleeder pump?

Mike
Old 05-22-2001, 04:14 PM
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hey, in my 84 944 does it have a high side and low side. i only see one next to the evaporator. is there another one?
Old 05-22-2001, 04:21 PM
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To pull the vacuum I used a $9.97 vacuume pump from Harbor Freight. One end plugs into my compressor, and I set it for 90 psi regulated and the other I mated to the charging hose that came with my retro fit kit. I also purchased a $3 vacume guage from Harbor Freight so I could check that I was sucking at 28. I ran mine for 1/2 hour, but from the looks of the above post I probably should have gone for more. Here is a link for the pump:

http://www.harborfreight.com/cpi/taf/Displayitem.taf?itemnumber=3952

Old 05-22-2001, 05:36 PM
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Verify that the receiver/dryer is installed with the direction of flow in the appropriate direction. A repair shop charged me $360.00 and stated I need a A/C control panel because the system would not take a charge. I got my 86na home and reversed the dryer, did it myself.(It would've cost too much to contest them in court).
Old 05-23-2001, 04:44 AM
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Thanks for the reply and link Scott R. I'll check it out. Thanks

Mike
Old 05-23-2001, 06:10 PM
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That el-cheapo vacuum pump works great. I made a brake bleeder with mine.
Old 05-24-2001, 02:52 PM
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Do you have to replace the compressor when you convert? I thought i saw some where that said you could just add some kind of oil and the new gas will work fine with the old stuff.
Old 05-24-2001, 03:34 PM
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i heard the same, just add the new oil,134 freon and it will be ok
Old 05-24-2001, 06:58 PM
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According to the Porsche tech bulletin, you must evacuate the system, drain the oil, and replace the valves, receiver/dryer, and o-rings on the dryer. The tech bulletin says nothing about the compressor.
In fact, after doing some light research on R134, I read that most of the problems with R-134 are correctable. Seals and hoses conditioned by R13 should not leak with r134, unless they are deteriorated. Apparently when "they" did tests on R134, they did it on a new AC system. It leaked. It was found subsequently that on older systems, the r13 conditioned the o-rings and hoses, sealing the porous material. The R134 doesn't leak (much) on older systems. The same holds true on compressor seals.
As I said, this is from amature research on the internet and articles I read. No real scientific data. Take it for what it's worth.

Old 05-24-2001, 11:24 PM
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