1) On my system, they filled with 134a to check for leaks. Evacuated it out and refilled with r-12 after determining the system was leak free. Since you live in Canada, I don't know if this is an option for you. If you come over to the US to get it done, I think your best bet is a custom a/c shop. One that does RV's, Classic Cars, and the like. They seem to appreciate the benefits of r-12 over 134a. Most car shops have ditched their r-12 equipment as it breaks since 134a is the dominant refrigerant now and are more interested in converting to 134a.

2) Running your system when it's low on refrigerant isn't a good idea. Yes, the low cut out will stop the compressor once it's threshold is reached, but refrigerant carries the lubricating oil through the system. If you're low on refrigerant, sufficient oil is not being carried through the system.

3) I believe the filters are usually installed on the suction line, before the compressor.

You may help hold your costs down by purchasing the parts before you make the appt with the a/c shop. Go ahead and get the rec-drier, new aux fan swx, low pressure cut out switch and the needed O-rings as well. Fastlane and other online vendors supply them. The filter can be purchased from ackits.com

Good Luck

__________________
"the simplest answer is usually the correct answer"

1991 190e, 2.6 (helga)
91,000 mi