If moisture is in the system, the system will be cold at the beginning but the moisture (ice) starts clogging up the expansion valve and the AC stops cooling. Low side pressure will be low or negative. The moisture usually is in the drier but for some reasons (possibly due to saturation and/or temperature changes) the moisture comes out of the drier.
The white stuff you see may be desiccant powder that comes from breaking down of the desiccant inside the drier.
Without seeing and touching the system myself, it is hard to say exactly what the white stuff you see from the sigh glass is. They may be just bubbles.
For R-12 system only, if the system is full, you see no bubbles except during acceleration, deceleration, and clutch kicking in/out.
To my knowledge, the mineral oil inside the system after conversion is just sitting there doing nothing.
Last edited by be459; 08-23-2001 at 04:03 AM.