On the oil in the dryer, my last one had a little flyer stuck in it that recommended 1 oz of oil. You just pour it down were the hose goes right before you install it. I have a big fat syringe I got down at a medical store that has tick marks on the side, you do not have to worry about spilling any oil or how much you got in there. If you have a clean system use PAG 40 oil, if you still have the old oil from the R12 use Ester. Don't mix Pag and Ester is something you read about all the time so avoid that. The old dryer should have oil inside it and you will see some leak out of the hoses when you pull the old dryer out. I have some rubber stoppers that I pop into lines to keep moisture out and oil in. Be sure to plug up the old dryer, oil will leak out if you turn it the right way.

Leave the dryer sealed and in a dry place until right before you are ready to install it. The goal is to avoid getting moisture in there before the system gets closed up. Remove the fittings from the old dryer and have new o rings standing by. Give the o rings a coating of the oil right before you slip them in. Be sure to get the hose lined up and push the fitting straight in, that will help avoid a pinch. Do not over tighten the nuts on the hoses, you can also crush an o ring if you get carried away.

You do not pull a vacuum on R134 systems because of freezing issues like you did on R12. Getting any moisture out is a benefit, but you are checking the integrity of the seals before adding coolant. I have been know to jumper the low pressure switch and do a red neck vacuum where you just start adding coolant instead of pulling a vacuum first. But I also knew that the system was tight before it was opened, I would do want to do that on one that was empty. Where did the coolant get out and is it fixed now is the concern there.

Regards,

Paul