I recently charged the AC system in my ALH TDI 84 Vanagon. Last September, I flushed each individual section of hose, the condenser and the evaporator. I put it all back together, including a new SD7V16 compressor (modified by me) and a new dryer. The modification involved "plugging" the RCV. I vacuumed the system and let it sit until a hot day this past April.
Then, I connected the manifold gauges and vacuumed it for two hours. I added R134a refrigerant based on the amount required for an MK4 Jetta which, totally was just shine of 3 cans for the Vanagon's system (12 ounces each, if I remember correctly).
Using a digital probe style thermometer in a vent, when the temp reached 35f at a pre-set point on the Temp Setting, I quit adding refrigerant. So, at that setting it cycles off at 35f and will cycle back on at 48 to 50f. The ambient Temp was 85f. The work was all done at engine idling.
Point is: as others have suggested, the system needs the required amount of refrigerant. Low, it will likely freeze-up especially in a high humidity situation. Too low and it will not cool. Too much and it will not cool very well. In my case, I had to feel in the dark to find the magic amount of refrigerant.
Plugging the RCV is necessary because the Thermal Expansion Valve in the Vanagon's system functions entirely different than the TXV in the MK4 Jetta.
Yes, cycling of the AC Compressor Clutch will shorten it's life. But, in the big box Van out on the highway on an 85f plus day in full Sunshine it will not be cycling very often.
So, to the OP, I suggest that you add a smidgen more refrigerant before installing another TXV. The low end suction pressure should be 35psi to 45psi with the high end somewhere above 200psi to about 250psi depending on the ambient temp. Also, we assume that the new compressor come pre-charged with oil.
