Can anyone lead me in the right direction on diagnosing this tk unit thanks

[REEFER_ATL608]

Hello fellow techs i have a 2007 thermo king sb200 and i would like to know how do
i preform a three way valve test .this unit needs refrigerant about every two weeks. There is no visible leaks, i checked for leaks with a leak detector and also put nitrogen in the system and still can not find any leaks. I preform a low side pump to 25 vac and suction side rises above 0 on
gauges within seconds.
Can anyone help thanks

[cadwaladr]

Throttling valve,there. Is a vent hole on the back of it test there,also compressor shaft seal maybe another leakage points plus the gaskets on the discharge manifold.

[REEFER_ATL608]

Hey thanks i will test the throttling valve.later today do i need to have a compound gauge or can i check it with my manifold gauge. Also i replaced the shaft seal already, throttling valve gasket, and the discharge manifold gaskets and it's still been loosing refrigerant

[cadwaladr]

There is a vent hole at back best tested with soap solution with unit not running

[REEFER_ATL608]

There is a vent hole at back best tested with soap solution with unit not running

thanks i will try this and let you know the out come