my rear evaporator went out so we replaced it and now when i am trying to charge the system the low side pulls a vaccum..what could this be? we have already replaced compressor, both xpansion valves, presure swithch, dryer

 

well only thing that can be pulling a vaccum is 2 things. you have a restriction. low on gas(almost empty or close to being empty). restriction could also be caused by the txv that has its bulb that senses defective lost its charge and caint open.

 

Make sure you didn't leave the protective plastic plugs or paper "stickers" on the openings of the new parts.