I could be wrong, it's been known to happen on occasion. I'm offering the best advice I can but the fact is that I haven't even lifted the hood on mine to see.

As far as converting, you really should evacuate and vacuum the system to make sure there isn't any left. There is likely still some in there somewhere.

BTW, I replaced a set of a/c hoses on a truck (chevy) the other day. I evacuated the system, then I vacuumed it for 3 mintutes. Then I watched to see if it would hold vacuum. It held 28" Hg for 2 full minutes. I disconnected teh machine and parked the truck, waiting for the work to get sold. When I brought it back in 1 1/2 hours later and pulled the bolt out of the compressor, yellow/green foamy oil came out under pressure. I had even turned the compressor by hand with the machine on it and no new pressure appeared.

So, yes. You need to vacuum the system before converting.

Clay