The newer cars I've had with R134a all are charged by weight per the factory manual. And they all lack sight glasses. I've read on forums that this is because a properly charged 134 system will always have bubbles flowing in the high side. Seems odd if they have a receiver/drier. That thing never fills with liquid???
I'm skeptical. My suspicious mind tells me it's because that's how they do it at the factory. Fast and simple, suck it down, fill it up, no running of the system required and no need for a sight glass. So no instructions on doing it other ways.
I've read that VW's with their variable displacement pumps and fancy "expansion" valve (I can't remember the correct term at the moment) can't be properly charged by pressure. No explanation why and again, no sight glass.
I've "topped off" my Dodge by pressures, contrary to the factory manual, and it seems to work fine.
Some day I'll get my Wag with a Vintage Air system running. Been a while since I looked at them but I recall the instructions say fill it with a certain weight. No mention of using the sight glass on the drier. I plan on keeping the factory in-line sight glass too just for the heck of it.
So, can anyone splain why one can't charge a 134 system using pressures and the sight glass?
How bout it Ed, you've installed a few systems. Wadayou do?