R12 to R134 I did it.
 

My 190 has not been holding a AC charge so I brought it to the dealer (they ended up being the least expensive when all was said and done. The shop manager assured me that the temp would be the same if not better than with the R12 in it.

I was doubtful but they said they would not put R12 in due to the cost and the environmental concerns. So I told them to go for it.

The temp today was 88 and fairly humid. So far so good. I had the fan on the lowest of 4 settings and the temp at max. I was comfy all the way to the body shop (25 miles). Yesterday I put the fan on the 2nd stting when the car was sitting for a bt in the sun and it cooled the car right down once I got to speed.

According to the hand test (putting my hand by the center vent) it feels quite cold. I would say as cold as it was with the old R12.

BTW, the manifold was shot so they replaced that, the dryer and switches.

So far so good.