Just a couple points on the discussion.
We have easily converted a thousand cars of numerous brands. We still do it because that is where the market went. We started doing conversions the first year R12 got taxed. In the beginning there were all kinds of horror stories due to potenial mixtures that would cause all kinds of problems. One concept was that the two oils would make a foam that would harden sort of like the stuff you squirt in walls that turns to styrofoam.
It turns out that the worse thing that seems to happen is poor air conditioning, maybe a few extra leaks. It is now thought that the mineral oil from the R12 system just moves around the system taking up space. It pools it the least turbulent areas and really does nothing. This is now the position of MACS ( the Mobile Air Conditioning Society). They are one of the testing services that register R12 handlers.
The other point has to do with evacuating systems, the concept has been resolved that evacuation only pulls gases from the system. Think about trying to suck the Coke out of a Coke Bottle vertically (without a straw). Won't happen, BUT, if you heat the coke and let it boil then one can easily suck off the steam. The boiling point of water is 212deg F at sea level. High in the mountains water boils at less than 200. In space, water boils at room temp (one of the reasons for pressuring space suits).
The point of evacuation is to take the system to outer space conditions and suck off the gasses this causes. This is mostly water that disolves in the A/C oil but also can be the liquid remains of arromatic flushes.
As it turns out, standard gauges are inadaquate to verify the level of vacuum that is appropriate. AND unless the vacuum pump is regularly maintained with regular changes of oil, the best of pumps will only go low enough on very hot days. Just sucking on it guarantees nothing.
Bosch Master, ASE Master, L1
33 years MB technician
Last edited by stevebfl; 07-05-2002 at 12:32 PM.