How do I remove the Ac oil in my 89 corvette when switching from freon to 134 . How much should be added and where?

I have upgraded or retrofitted older cars with r134a before with the ester oil and never had any problems with the refrigerant working with the old oil, as long as you put a few ounces of the new oil in.

The kit for r134a conversion from R-12 has everything you need to upgrade without removing all of the old oil.

Of course, in the early days of r134a conversion in the early 1990s there were people who recommended that you take the whole system apart, compressor, piping, receiver drier, etc. and replace the receiver drier and dump out the old oil.

In my opinion, this is a very expensive proposition, and good to excellent air conditioning can be had by following the R134a conversion kit instructions and installing 2 or 3 cans of refrigerant into your system.

This can be done by yourself.

Watch, if you're in California, you have to return empty cans of R134a to the store because they say that it is harmful to the environment and they want to keep track of it.

Good luck staying cool with R134a.