From a 77 Camaro Type LT 305 ... If I get no psss when I press the low side schrader valve, am I still concerned about trying to recover R12 before doing any work on the system. I am looking to replace the compressor and convert to R134. The system has not worked in better than a year ... I plan to leak detect after swapping the compressor ... Any advise would be helpful .... Thanks in advance ... sdtsdt

Here in the USA it shoukd be recovered, but I would just crack a line and make sue it is empty and go ahead and do what you need to do. If you push the shrader and nothig comes out you should be okay, but you could still have some puddled in the accumulator, condensor or evaporator that could boil and escape after sitting and escape when the line is opened so just loosen the line untill it hisses if even does and don't open anymore until it stops.

say goodbye to the ozone hole remedy. Even after science was sure R12 was causing the problem, the ozone hole continues to grow.

If you push in the schrader valve and there is no pressure, then there is no R-12 left in the system. With no R-12 in the system, there is nothing left to recover. Make sure you replace the dryer, orifice tube (Chevy was using a CCOT system in 77 weren't they?) and flush the old oil out of the system. If it holds a vacuum, refill it with 134a. You will only use 75% of the R12 system charge. Then you are ready to ride in A/C comfort!

You don't have to remove the oil out of the system when you do a conversion, it is 100% impossible to remove the oil unless you replace all the components in the system. When the any components are replaced just be sure to use Pag oil or Ester oil which combines with the original r12 oil just fine and then recharge the system to the previously recommend amount of 75-80% of the r12 system charge.

if you have no pss when on pushing on valve than it is empty. so you dont need to worry about reclaiming r-12. when you replacing air compressor blow out lines with air. to get warranty with compressor change accumulator. also i would reseal each line with new o-rings. thinking of year of car.draw a vacumn into system and wait a hour to make sure it doesnt drop in pressure. see how much new compressor needs of oil and add it. also put a leak detector dye in it. than charge it up. to about 25-30 on low side.at idle.

Thanks guys .... All of a sudden I feel brave ... I will post back later, probably this coming weekend, hopefully with tales of success, but, if necessary, with more questions... I appreciate the assistance and the advice ....

Thanks,
Steven

You don't have to remove the oil out of the system when you do a conversion, it is 100% impossible to remove the oil unless you replace all the components in the system. When the any components are replaced just be sure to use Pag oil or Ester oil which combines with the original r12 oil just fine and then recharge the system to the previously recommend amount of 75-80% of the r12 system charge.
Sure you don't have too, but you can get most of it out. It is always best to get as much oil as possible (you'll never get 100% out). The oil can be removed by flushing the system with an A/C flush apparatus. Leaving the old oil in the system just doesn't make sense to me. I'm not saying you can't leave the oil in there and have an operating system, but it could cause problems and why risk having problems with all of your new parts? If your going to do something, its worth doing right.

Flushing the old oil out of the system used to be the standard procedure because, as Tom says, it only makes since. But many people found that the old mineral oil permeated the hose over time and actually helped seal the older hoses so that when R134a was introduced into the system it was less likely to leak. R134a is a smaller molecule and is more prone to leaks. It is why they use a different hose and fitting combination with R134a. I wouldn’t flush the hoses unless the system has been wide open for a while or it is contaminated.
Gary