68 vette ac compressor dragging down at idle.

[seagames35]

68 vette small block ac system rebuilt charged with R12 and ran one time with rebuilt a6 compressor and blew seal. Installed new ac compressor no issues when charging had 46 degrees. Next day when hot, compressor works fine till idle and compressor tries to lock up and belt squeals. So every time I try to idle with ac on compressor drags and belt starts to slip. I put in 50 oz of R12.

[JohnHere]

Some questions: I don't have the refrigerant specs for your car, but 50 ounces sounds about right. Did you get that from an under-hood decal or did you charge it using the sight glass? How much oil did you put in? What were the pressures at 1,500 to 1,800 RPM, and what was the ambient temperature in front of the grille? Did you replace the condenser and receiver/dryer? What was the reason for the compressor replacement?