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Discussion Starter #1
I got the A/C recharged this morning. Tech ran the high side pressure up to 150 and stopped. I asked him why he stopped and he stated that 150 was the high side operating pressure for this system. I did not agree, with my understanding was to charge the system until all bubbles are out of the sight glass, and then you are done. Who is correct? I think I did not get all of my freon back. Opinions, please?


Steve Leslie, 65 coupe in restoration. 302, toploader, A/C, disc brakes, bench seat

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I can answer your question, but I need a little more information. Did you charge it with R-12 or R-134A? What was the ambient temp when it was charged, and what was the engine RPM?

Jim Vogel
Tallmadge, Ohio

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Discussion Starter #3
Charged it with R-12. Temperature of outside air was about 68 degrees. Engine was idling at about 650 RPM.



Steve Leslie, 65 coupe in restoration. 302, toploader, A/C, disc brakes, bench seat

http://albums.photopoint.com/j/View?u=1571478&a=12535662&p=46267978&Sequence=1.jpg
 

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The best way of determining correct charge when it is not known is by monitoring superheat and/or subcooling along with pressures. I won't give a definition of those terms here, but if you ask I will. Anyway, the bubbles in the sight glass method is a decent rule of thumb with R-12, but doesn't usually work with R-134A. Run your car steady state at about 2000 rpm for a couple minutes with the windows open and the fan on high, and observe the sight glass. If you have bubbles, it's possible you may be undercharged, but in my experience, 150 psi on the high side at 68 degs isn't too far out of line. Keep in mind that this system has to operate at much higher ambients that this, and you want to make sure that it will not trip on the high pressure switch at any ambient condition that you may encounter. Have you measured louver temps?

Jim Vogel
Tallmadge, Ohio

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From my experience with R-12 systems, if you have a few bubbles in the sight glass at idle it's OK, but with the RPM up around 1500 to 2000 it should look like a liquid. Another tip that I got from an experienced A/C man said to make sure the suction line was cool and sweating all the way back to the compressor, as that is what also cools the compressor. On a really hot day I've seen 250-275 psi on the compressor discharge line.

Jon Sherar/ 67 Fastback
 
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