Let's get something straight right now; you DO NOT charge a system using the liquid line sight glass. Period.
The only way to check a TXV system's charge is by measuring the Subcooling. Period.
A full glass indicates there is liquid at the glass...that's it. The Subcooling could be low. The Subcooling could be high. Or, the Subcooling could be just right. But you'll never know until you check the sub-cooling.
A bubbling sight glass indicates there is flash gas at the glass...that's it. It may be bubbling because there's a restriction in the line, or because it's low on charge. But you'll never know until you check the Subcooling.
What do I use a liquid line site glass for? The moisture indicator. That's it.
What do I use to check the charge? Subcooling. Period.
