1990 740GL Regina - on its way back to really roadworthy...

So it's hot this time of year and my AC is not working. I remember pulling the belt off (have a replacement handy) and I tested it by shorting the low-pressure connection to bypass the switch. The compressor clutch engaged (belt still off) Based on the FAQ, this means it has a low charge.

In an attempt to be scientific, I thought I could just grab some adapters for temporary installation and hook up my R-134a gauge set to see exactly how high or low the R-12 charge level is. Much to my chagrin, the adapter fittings seem like they will vent some of the charge as I screw them on - possibly quite a bit - so I didn't try to even install the hoses

I have the same situation on my other project volvo that is much farther from roadworthy, so I really want to figure out a way forward with the one car. I need to determine if I should vent the last 10psi out of the system and retrofit or if I can get it working again by topping off a system that's just a little low. Every seal leaks, and after 35 years, I would be shocked if the charge was higher than 60%, but simply topping off with one or two can of R-12 is a lot cheaper than a full retrofit and will work better by all reports I've seen. At this point, no shops I've called have any kind of R-12 equipment anymore, so nobody can recover whatever amount is left in them.


Are there any good guides on the fittings involved for the retrofit or the connections? It seems like I'm missing something and that the fittings can't have been designed to leak when being connected or disconnected.


Cheers,
Will