APU and AC trouble

I have a pro-heat 1st gen? apu. Since I bought the truck (8 years ago) I have been unable to fix the ac which does not work. (everything else works including heat). I tore apart the bunk yesterday and evacuated and recharged the AC. The low side PSI is reading a negative vacuume with the compressor running, high side is around 100 psi (80F outside). The evaporator bulbs soldered onto and going into the evaporator core are both frosted. Putting a heat gun on them made no changes. Everything I am reading is that the TVX valve may be stuck, but I am absolutely unable to find anything that remotely looks like a tvx valve, I did find the filter drier which has the capillary copper tubes, coming from the sensing bulbs and going into it. I am not sure what to do next, i've tried tapping on everything, heating up parts, but no difference in colder air temp. Everything including the evaporator fan and the condesor(?) fan outside of the truck appears to be working properly... I hate quitting on DIY projects but I am totally stumped. I dont want to chop open the system and replace the drier when the problem is likely something simple or totally unrelated. *ANY help or advice would be appreciated.

 

also reading that despite the compressor starting/running that a bad or weak capacitor could cause a negative vaccum