i didn't hear anything about a liquid line filter, gauges or vacuum pump. so you guys just connected the lines and turned it on. no system is that 'plug-n-play'. standard service procedures need to be followed and that's why it needs to be done by a professional. it probably is still low on freon, but it also needs to have a liquid line filter/drier in the small line. it could already be installed in the outside unit. if the lines are precharged with refrigerant and there is a drier already installed, maybe a vacuum wouldn't be required, but i'm skeptical. in any case, the final charge needs to be determined by technical means utilizing a strap on thermometer and pressure gauges. if you do not have instrumentation, you are still going to need to hire someone to balance it.