Dannoman

I am troubleshooting my 14 sierra ac system so I bought a set of gauges and a vac pump. I hooked them up started truck and turned on ac to high setting and neither high side or low side show a pressure and the compressor didnt kick on but when I hook up cheap gauge on my refrigerant can to the low side the pressure goes up to like 85. Not sure if just got a bad set of gauges and manifold or what