Low side is high and high side is low, there may be a blockage or weak compressor. I'm assuming that the ambient temp is high though, you'd only see low side 75 if it's really really hot out or the system is very over charged. But under both conditions you'd have high side pressures much higher than 175, which to me would indicate that 134a isn't passing from low to high side correctly, whether it be a blockage or a weak compressor I don't know. You should evac the system and see if you can inspect the receiver drier for funk and gunk on the filter bag for the desiccant.