Charge Determination R134a TXV Automotive System

[motoboy]

I am trying to determine the charge amount for a R134a TXV AC system by measuring condenser subcooling.
My question is how much subcooling is ideal(it has a reciever dryer so I'm assuming not a lot).

The other thing that I'm having a hard time wrapping my mind around is what is the ideal test condition, I'm assuming the worst case ambient temp (120F in this case) with blower fan on high and vents set to fresh air would be ideal. I'm also assuming running the condenser fan on high would be ideal.

From what I gather the ideal charge is when the receiver dryer is full and and the bottom of the condenser is just starting to fill with liquid?

What then happens when this system is run in a much cooler ambient than my test case? Does the condensor flood with liquid and the system cycle off the high pressure side of the binary switch.

Please point out where I'm wrong because something isn't adding up.
Thanks

 

[hollandhvac]

Have you got not sight glass in the system? When I had the systems filled by a rep. company the man was only looking at the sight glass if that was full i.e. no bubbles.

 

[ccjersey]

Under the "much cooler" conditions you describe, the evaporator load may be just a high as normal in which case the condenser would not fill with liquid.

If the evaporator load is decreased significantly under the cooler conditions, there will be increased filling of the condenser with liquid refrigerant and increased subcooling, but short of the point where the condenser is almost completely filled with liquid, the "much cooler" conditions should prevent much of an increase in head pressure and certainly not cause the compressor to cycle on the high pressure safety.